These juicy, crispy-edged smash burgers are topped with sweet, golden caramelized onions, melty cheddar cheese, fresh lettuce, and a punchy garlic herb aioli—all tucked into a soft brioche bun. I love how each layer adds something irresistible: the crispy beef edges, the rich onions, the tangy sauce. It’s everything I want in a homemade burger.

Why You’ll Love This Recipe

I love this burger for how fast and flavorful it is. The smash method gives me that golden, crispy crust on the patties without drying them out. The slow-cooked onions add depth and sweetness, and the garlic herb aioli lifts everything with a bold, herby finish. This recipe hits that perfect mix of comfort and gourmet without being fussy.

Ingredients

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

For The Caramelized Onions

• 2 medium sweet onions, thinly sliced

• 4 tablespoons unsalted butter

• Pinch of salt

For The Burgers

• 1 pound lean ground beef (I use 93% lean for the best balance of crispness and juiciness)

• 1 teaspoon kosher salt

• ½ tablespoon canola oil or vegetable oil (any high-heat oil will work)

• 1 tablespoon unsalted butter

• 4 slices sharp cheddar cheese (or use any cheese I like, such as American, Swiss, or Gouda)

• 4 brioche burger buns

• Leafy green lettuce (such as butter lettuce or romaine), for topping

For The Garlic Herb Aioli

• ½ cup mayonnaise

• 2 tablespoons fresh basil, finely chopped

• 2 tablespoons fresh parsley, finely chopped

• 1 tablespoon fresh rosemary, finely chopped

• 2 garlic cloves, minced or grated

• Freshly cracked black pepper, to taste

Directions

Make The Caramelized Onions

1. I start by slicing the onions as thin as possible for even cooking.

2. In a large skillet over medium-low heat, I melt the butter and add the sliced onions with a pinch of salt.

3. I stir them occasionally and let them cook slowly for 20 to 30 minutes, until they’re soft, golden, and deeply caramelized. If they start to dry out too much, I add a splash of water or a touch more butter.

4. Once done, I set them aside or refrigerate if making ahead (they keep well submerged in a bit of oil).

Make The Garlic Herb Aioli

1. I combine the mayonnaise, chopped basil, parsley, rosemary, garlic, and black pepper in a bowl.

2. I mix it until smooth and creamy, then refrigerate it until I’m ready to use. This sauce tastes even better after sitting for an hour or more.

Cook The Smash Burgers

1. I divide the ground beef into 4 equal portions, gently forming them into balls without overworking the meat.

2. I preheat a cast iron skillet or griddle over medium-high heat for at least 5 minutes until it’s very hot.

3. I brush the skillet with oil and add half the butter.

4. I place one ball of beef onto the hot skillet and immediately smash it down hard using a flat spatula, burger press, or the bottom of a jar. I try to make the patty about ½-inch thick with ragged edges for maximum crisp.

5. I season the top with salt and let it cook undisturbed for 2 to 3 minutes until the edges are browned and crisp.

6. I flip the patty, season the other side, and cook for another 1 to 2 minutes.

7. I place a slice of cheddar on top and cover briefly (if needed) to melt the cheese.

8. I repeat with the remaining burgers.

Assemble The Burgers

1. I lightly toast the brioche buns, then spread garlic herb aioli on the top and bottom halves.

2. I add a few lettuce leaves to the bottom bun, then place the cheesy burger patty on top.

3. I spoon a generous amount of caramelized onions over the patty and cap it with the top bun.

4. Serve immediately while everything is hot and melty.

Servings And Timing

Servings: 4
Prep Time: 20 minutes
Cook Time: 40 minutes
Total Time: 1 hour

Variations

• I swap the cheddar with Swiss, Gouda, or pepper jack when I want a twist on flavor.

• Sometimes I add crispy bacon or sautéed mushrooms to the burger for more texture.

• If I want some heat, I stir a bit of sriracha or smoked paprika into the aioli.

• I’ve made this with arugula instead of lettuce for a peppery bite.

• When watching carbs, I skip the bun and turn this into a burger bowl over greens.

Storage/Reheating

• I store leftover patties and caramelized onions separately in airtight containers in the fridge for up to 2 days.

• The aioli stays fresh in the fridge for up to 4 days.

• To reheat the patties, I warm them gently in a skillet over medium-low heat with a splash of water and cover them until heated through.

• I always reassemble the burger fresh after reheating so the buns don’t get soggy.

FAQs

How Do I Get The Crispy Edges On Smash Burgers?

I use a very hot skillet or griddle and smash the beef ball immediately upon contact. I don’t move it around, which lets a golden crust form. The edges crisp up beautifully when I resist the urge to flip too soon.

Can I Use Pre-Made Patties Instead Of Forming My Own?

I don’t recommend it. Pre-made patties are often too thick and won’t smash properly. I always form my own from loose ground beef to get that thin, crispy finish.

What Type Of Onions Work Best For Caramelizing?

Sweet onions like Vidalia or Walla Walla are my go-to for the best flavor. But yellow onions work great too—they just take a little longer to get sweet and tender.

Can I Make Any Of The Components Ahead Of Time?

Yes. I often caramelize the onions a day or two ahead, and the aioli can be made up to 3 days in advance. That way, burger night is mostly just cooking and assembling.

What’s The Best Cheese For Smash Burgers?

I usually use sharp cheddar because it melts well and adds bold flavor. American cheese is classic for that melty texture. I pick whatever matches the mood or toppings I’m using.

Conclusion

These caramelized onion smash burgers bring together everything I crave in a homemade burger—crispy, juicy beef, deeply sweet onions, and a tangy, herb-filled aioli. The method is simple, the flavor is restaurant-worthy, and the whole meal comes together in about an hour. It’s one of my favorite ways to elevate burger night without adding much effort.