Caramelized Onion Smash Burgers.

This caramelized onion smash burgers are sponsored by St Pierre! I’m so excited to be partnering with them this summer to bring you delicious recipes.

Hello summer! Is there anything better than a flavorful smash burger?!

caramelized onion smash burger

I think not. These are a DREAM. 

Burgers with crispy, crunchy edges, smothered in cheese and caramelized onions and served on top of buttery brioche bread. 

st pierre brioche buns

Today, I’m so excited to be partnering with St Pierre! We love love love their brioche bread products so much. You probably recognize their buns in so many of my sandwich recipes – I’ve used them for years and they are seriously the best. These are my go-to store bought buns for sure. 

st pierre brioche buns

The St Pierre Burger Buns are perfect to use if you’re entertaining or simply grilling dinner for yourself. The buns are buttery and pillowy. I ended up throwing mine on the grill for an extra toasty taste. The texture is light and airy, but the buns are sturdy enough to hold a burger, which creates the absolutely PERFECT bite of texture. They totally elevate a regular old burger or sandwich and take the meal to next level!

caramelized onion smash burger set up

I’m thrilled to share this caramelized onion smash burger which is absolutely LOADED with flavor and served on the brioche burger buns. 

burgers on the grill

I don’t think it’s any secret how crazy I am for smash burgers. I mean, they are easily my favorite burger that we make in this house. Same goes for Eddie and even the kids are into them now too. In fact, for two weeks Max kept saying he wanted a “burger with cheese and lettuce.” I assumed he either saw it in a movie or read about one in a book. But I loved that it was his first real “craving” and can totally relate.

caramelized onions

Who doesn’t crave a smash burger in the summer?!

I wish I could eat one right this instant.

smash burgers

So, caramelized onion smash burgers were born!

caramelized onion smash burger

To get the classic smash burger texture, using a cast iron skillet is best. In previous years you’ve seen me make them in my kitchen and sometimes I’ve even put the cast iron skillet directly on the grill and use it there. This year, I’m using the griddle attachment on my actual grill, which is perfect because I can smash the burgers directly on the grill. AHHHH!! 

How amazing is that?

caramelized onion smash burger

It definitely makes things easier. But if you’re just using the skillet, cast iron is great because it gets HOT. And that’s what you want. A hot skillet. A round of beef. Then use smash it into the skillet using a burger press, the bottom of a glass or the flat end of a meat tenderizer. The edges get crispy and golden and the burger cooks in all that goodness.

Oh and did I mention that we add butter to the pan too?


caramelized onion smash burger

I like to smother said burgers in cheese (your favorite variety works here; my usual is sharp cheddar or gouda!) and then pile them high with caramelized onions. 

There’s also a garlic herb aioli slathered on the buttery St Pierre brioche bun and some crisp refreshing lettuce to really take things over the top. 

caramelized onion smash burger

I can’t even handle these beauties! They are perfect for the Fourth of July and will take your menu over the top.

caramelized onion smash burger

Caramelized Onion Smash Burgers

5 from 11 votes
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Yield: 4 people
Caramelized Onion Smash Burgers
Total Time:
1 hr
These caramelized onion burgers are loaded with flavor, smothered with cheese and caramelized onions and topped with garlic herb aioli.
caramelized onions
  • 2 medium sweet onions, thinly sliced
  • 4 tablespoons unsalted butter
  • pinch of salt
  • 1 pound lean ground beef, I like 93%
  • 1 teaspoon salt
  • 1/2 tablespoon canola or vegetable, or any high heat oil
  • 1 tablespoon unsalted butter
  • 4 slices sharp cheddar cheese, or your favorite cheese
  • 4 St Pierre Brioche Burger Buns
  • leafy green lettuce, for the burgers
garlic herb aioli
  • ½ cup mayonnaise
  • 2 tablespoons chopped basil
  • 2 tablespoons chopped parsley
  • 1 tablespoon chopped rosemary
  • 2 garlic cloves, minced
  • freshly cracked black pepper
caramelized onions
  1. Thinly slice the onions. Heat a large skillet over medium-low heat and add the butter. Once melted, add in the onions with a good pinch of salt. Stir to combine everything. Cook, stirring often, for 20 to 30 minutes, until the onions caramelize. I love a classic, slowly caramelized onion, but if you’d like to speed up the process, you can add a pinch of sugar while cooking. You can also make these ahead of time and store them sealed in the fridge, submerged in a bit of olive oil.
  1. Divide the beef into 4 equal parts. I like to form mine into balls so they smash into a more circular burger.
  2. Heat a large cast iron skillet or your grill griddle over medium-high heat. You want it to be hot, so heat it for at least 5 to 10 minutes.
  3. Once it's hot and your burgers are ready to go, quickly brush the skillet with oil and place half of the butter on the skillet. It will smoke, so work quickly! Place one of the balls of beef on the skillet and smash it down with a burger press, spatula, mason jar, etc - once or twice. You want it to be about 1/2 inch in thickness (or a little less) and want to try and smash it only 2 or 3 times. Season it with salt and pepper and repeat with the rest of the beef. Cook the burgers for 2 to 3 minutes and then flip, season with salt on the other side and cook for 2 minutes more. Add the cheese and let it melt for just 60 seconds or so.
  4. Remove the burgers from the heat. Spread the aioli on the buns and top with a piece of lettuce. Add the burger on, along with the caramelized onions. Serve immediately!
garlic herb aioli
  1. Whisk together the ingredients until combined. You can make this ahead of time and store it in the fridge.

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caramelized onion smash burger