Trust me when I say, once you try these Buttery Roast Beef Sliders with Caramelized Onions Recipe, you’ll want to make them again and again. Picture tender roast beef, melty cheese, and sweet, jammy onions all smothered with garlic aioli and baked inside buttery slider buns. They’re simply irresistible!

The image shows a close-up of two stacked sandwiches on a wooden board. Each sandwich has three main layers: the top and bottom are golden brown toasted buns sprinkled with sesame seeds and seasoning, the middle layer is melted light yellow cheese with caramelized onions that are juicy and golden, and there is a layer of thin slices of cooked meat underneath the cheese. Some melted cheese and onions are dripping out from the sides, making the sandwich look rich and full. The background is dark, and the wood texture underneath contrasts with the food. photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I can’t get enough of these sliders! They hit every savory note just right and bring a cozy, comforting vibe to any meal or gathering. Seriously, these are game changers for your next party or even a weeknight treat.

Flavor Explosion: Sweet caramelized onions balance perfectly with savory roast beef and rich garlic butter.
Multipurpose: Great for game days, casual get-togethers, or even a satisfying family dinner.
Homemade Touches: From scratch garlic aioli makes these sliders feel extra special and fresh.
Perfect Texture: Soft slider buns brushed with garlic butter deliver that irresistible buttery crunch on top.

Ingredients & Why They Work

Choosing the right ingredients is key here. I always opt for Hawaiian slider buns for their softness and sweetness—they hold up beautifully without getting soggy. And fresh yellow onions? They’re essential to achieving those perfect caramelized layers that elevate every bite.

Flat lay of a cluster of 3 large yellow onions, thinly sliced in a small white ceramic bowl, a small white bowl of unsalted butter cubes, a small white bowl with olive oil, a small white bowl of light olive oil, a clean large whole brown egg with uncracked shell, a small white bowl with Dijon mustard, a single fresh garlic clove, a small white bowl of fresh lemon juice, a small white bowl with kosher salt, a small white bowl with brown sugar, a small white bowl with finely shredded mozzarella cheese, a stack of thinly sliced deli roast beef, a neat pile of sliced provolone cheese, a cluster of 12 Hawaiian slider buns halved horizontally, a small white bowl with Worcestershire sauce, a small white bowl with poppy seeds, a small white bowl with white sesame seeds, a small white bowl with garlic powder, a small white bowl with dried minced onion, a small white bowl of freshly cracked black pepper, all arranged symmetrically on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted butter: Brings creamy richness to the caramelized onions, garlic butter sauce, and au jus without overpowering.
Olive oil: Helps caramelize the onions gently without sticking or burning.
Yellow onions: Their sweetness develops beautifully during slow cooking to deepen the flavor.
Kosher salt: Enhances flavors evenly without clumping.
Brown sugar: Optional but speeds up caramelization and adds a touch of sweetness.
Beef broth: Used in the au jus and for deglazing the onions to maximize savory depth.
Egg yolk: The creamy base for our homemade garlic aioli that adds a fresh zesty punch.
Dijon mustard: Adds subtle tang and helps emulsify the aioli perfectly.
Garlic: Gives the aioli and garlic butter sauce that irresistible aromatic quality.
Lemon juice: Brightens the aioli to balance richness with a little zing.
Light olive oil or neutral oil: Keeps the aioli smooth and silky without overpowering flavor.
Better than Bouillon Beef Base: Packs a punch in the au jus, providing richness and authentic savory notes.
Worcestershire sauce: Adds umami complexity to both the au jus and garlic butter sauce.
Slider buns (Hawaiian rolls preferred): Soft, sweet, and perfect for soaking up all those delicious flavors.
Deli roast beef: Tender, thinly sliced—key to that melt-in-your-mouth slider experience.
Melty cheese (like provolone, Swiss, or muenster): Brings gooey, creamy texture that pairs wonderfully with beef.
Shredded mozzarella: Adds extra cheesy stretch and indulgence.
Poppy seeds and white sesame seeds: Give the garlic butter sauce a subtle nutty crunch and interesting texture.
Garlic powder and dried minced onion: Pack additional layers of flavor in the garlic butter brush-on sauce.
Freshly cracked black pepper: Accentuates all the savory elements with a mild kick.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

The beauty of these Buttery Roast Beef Sliders with Caramelized Onions Recipe is how easy it is to tailor them to your tastes and occasion. Whether you want to swap cheeses, go lighter on the aioli, or amp up the savory notes, there’s plenty of room for creativity!

Vegetarian Variation: For a delicious meat-free version, try replacing roast beef with grilled portobello mushrooms. The caramelized onions and garlic butter sauce add plenty of flavor to keep these sliders satisfying.
Quick and Easy Option: When time’s tight, jazz up mayo with garlic, lemon, mustard, and a pinch of salt in place of making aioli from scratch, then skip the caramelized onions for speedy sliders. I love this shortcut on hectic weeknights!
Cheese Choices: Provolone, Swiss, or muenster all melt beautifully here—try mixing two types for an extra cheesy experience. In a pinch, shredded mozzarella alone works well too.
Seasonal Twist: Add a handful of fresh arugula or baby spinach after baking for a pop of peppery freshness and color. It balances the rich, buttery flavors perfectly.
Make Ahead Tips: Assemble your sliders a day or two in advance without the onions or garlic butter brushed on top, then add them right before baking. It saves time while keeping sliders wonderfully fresh and flavorful.

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A woman's hand is holding a sandwich made with a toasted, golden-brown sesame seed bun, dripping with thick brown gravy. Inside the sandwich, there are multiple layers of soft, thin slices of cooked meat and melted cheese with a creamy texture, visible just under the bun. Below the sandwich, a white bowl filled with rich brown gravy has some gravy dripping down its side onto a dark wooden surface. Behind the bowl, several more sandwiches with the same sesame seed buns, meat, and cheese are stacked, showing their melted cheese and crispy textures. The whole scene is set on a white marbled surface with a blurred dark shirt in the background, capturing the warm, messy, and inviting aspect of the dish. photo taken with an iphone --ar 2:3 --v 7

Step 1: Slowly Caramelize Those Onions to Sweet Perfection

Start by melting 2 tablespoons unsalted butter and 1 tablespoon olive oil in a large skillet over medium-low heat. Toss in your thinly sliced yellow onions, sprinkle with ½ teaspoon kosher salt and 1 teaspoon brown sugar (this helps speed up the caramelization). Let them cook low and slow, stirring occasionally, for about 45 minutes until they turn soft, deeply golden, and jammy. Towards the end, splash in 2 tablespoons beef broth to deglaze the pan, scraping up every bit of that flavorful goodness. Set these aside—they’re going to be the sweet, savory highlight of your sliders.

Step 2: Whip Up Creamy Homemade Garlic Aioli

In a small bowl, whisk 1 large room temperature egg yolk with 1 teaspoon Dijon mustard, 1 finely grated garlic clove, and 1 tablespoon lemon juice until smooth. Slowly drizzle in ½ cup light olive or neutral oil while blending with an immersion blender or whisking vigorously, until the mixture thickens into luscious aioli. Season with kosher salt to taste and set aside. If you’re short on time, simply stir garlic, mustard, lemon juice, and salt into mayonnaise for a quick alternative.

Step 3: Simmer the Rich Au Jus Sauce

Melt ¼ cup unsalted butter in a medium saucepan over medium heat. Stir in 1 tablespoon Better than Bouillon Beef Base, 2 cups beef broth, and 2 teaspoons Worcestershire sauce. Let it gently simmer for 20 minutes, reducing by about half and thickening slightly. The sauce will darken and concentrate in flavor—keep it warm for serving alongside your sliders as a savory dipping delight.

Step 4: Toast the Bottom Slider Buns

Preheat your oven to 350°F. Slice 12 slider buns horizontally but keep the halves connected. Arrange the bottom halves cut-side up on a parchment-lined baking sheet. Lightly brush with melted butter or a bit of your garlic aioli. Toast for 5 minutes until just golden and slightly crisp—this gives the perfect base that won’t get soggy under all those delicious toppings.

Step 5: Layer Up the Good Stuff

Spread a generous layer of garlic aioli over the toasted bottom buns. Pile on about ½ pound of thinly sliced deli roast beef in 2 to 3 hearty layers. Top each slider with 12 slices of your favorite melty cheese (provolone, Swiss, or muenster all work beautifully), then sprinkle with ½ cup shredded mozzarella for that irresistible gooey finish. Spoon 2 cups of the caramelized onions evenly over the top—these add sweet, savory depth you’ll love.

Step 6: Top and Brush with Garlic Butter Magic

Place the top halves of the buns over your loaded sliders. In a small bowl, combine 6 tablespoons melted unsalted butter with 1 teaspoon Worcestershire sauce, 1 tablespoon poppy seeds, 1 tablespoon white sesame seeds, ½ tablespoon garlic powder, ½ tablespoon dried minced onion, ½ teaspoon kosher salt, and freshly cracked black pepper to taste. Give these rolls a generous brush of this flavorful garlic butter sauce—it’s what takes these sliders from delicious to unforgettable.

Step 7: Bake to Delicious Perfection

Cover your sliders loosely with foil and bake for 10 minutes, allowing the cheeses to melt and the flavors to meld. Remove the foil and bake for another 10 minutes, or until the tops are beautifully golden brown and perfectly toasted. Your kitchen will smell amazing!

Step 8: Serve Warm with Au Jus for Dipping

Slice carefully between each roll to separate the 12 sliders. Serve them warm alongside bowls of the rich au jus sauce for dipping. The combination of tender roast beef, melty cheese, sweet caramelized onions, and buttery garlic sauce dipped in savory jus? Absolutely irresistible.

Top Tip

Getting the most out of your Buttery Roast Beef Sliders with Caramelized Onions Recipe is all about patience and layering flavors thoughtfully. Here are some tried-and-true tips to make your sliders irresistibly perfect every time!

Slow Caramelization: Taking the full 45 minutes to caramelize the onions low and slow is worth every second — it develops that deep, jammy sweetness that makes these sliders truly special.
Garlic Aioli Magic: I learned that making the aioli from scratch really elevates each slider. Even if you're short on time, jazzing up a good mayo with garlic, lemon, and Dijon keeps it flavorful.
Butter Brushing Technique: Don’t skimp on the garlic butter brushed on the top buns before baking — it adds a beautiful gloss, poppy seed crunch, and flavor punch that makes these sliders unforgettable.
Avoid Sogginess: Toasting the bottom halves of the buns before assembly keeps everything nicely crisp and prevents soggy bread once the beef and onions are piled on.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

A tan baking tray holds five slices of light yellow bread with a soft texture. Each slice is spread with a layer of creamy white mayonnaise, which is smooth with small bits of green herbs mixed in. The slices are arranged close together, with three on the bottom and two on the top, placed on a white marbled surface. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

A sprinkle of fresh thyme or finely chopped parsley on top adds a lovely herbaceous note and color contrast. For a little extra zing, serve with pickled jalapeños or crisp dill pickle slices on the side. A dash of freshly cracked black pepper on the finished sliders also highlights the savory flavors beautifully.

Side Dishes

Complement these sliders with classic sides like crispy sweet potato fries or a crisp green salad with a tangy vinaigrette to cut through the richness. Creamy coleslaw or a simple cucumber salad also make refreshing companions, balancing the buttery, cheesy goodness.

Make Ahead and Storage

Storing Leftovers

Store any leftover sliders in an airtight container in the refrigerator for up to 3 days. Keeping them sealed well helps preserve that beloved moist yet tender texture.

Freezing

You can freeze the assembled sliders before baking (without the caramelized onions and garlic butter topping) for up to 1 month. Wrap them tightly in plastic wrap and then aluminum foil to prevent freezer burn. When ready, thaw overnight in the fridge before proceeding with onions, garlic butter, and baking.

Reheating

Reheat leftovers in a 375°F oven for about 10 minutes to warm through and refresh that just-baked texture without turning soggy. Serve warm with the reserved au jus sauce for dipping — it’s just like fresh!

Frequently Asked Questions:

Can I make these sliders ahead of time?

Absolutely! You can assemble the sliders up to two days in advance without adding the caramelized onions or garlic butter on top. When ready to serve, add those and bake as directed for fresh, delicious sliders.

What type of cheese works best?

Can I substitute the Better than Bouillon beef base?

Yes, you can substitute with any beef bouillon paste or concentrate you have on hand. Just adjust the seasoning to taste to keep that rich, savory au jus flavor.

How do I prevent soggy buns?

Toasting the bottom buns before assembly is key. Also, baking covered loosely with foil helps melt the cheese without drying out the sliders, keeping everything tender but not soggy.

Final Thoughts

Making these Buttery Roast Beef Sliders with Caramelized Onions is like wrapping up comfort, flavor, and a little bit of magic in soft, buttery buns. Whether it's game day, a cozy family dinner, or a gathering with friends, these sliders bring people together with each melty, savory bite. I hope you enjoy crafting and sharing them as much as I do — happy cooking!