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Smash Burgers with Caramelized Onions

Smash burgers with caramelized onions deliver crispy, deeply browned edges and a juicy, thin patty topped with melty American cheese. Slow-cooked onions become jammy and deeply golden, then get piled high for sweet, savory burger perfection.
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Prep Time 25 minutes
Cook Time 30 minutes
caramelizing 40 minutes
Total Time 1 hour 35 minutes
Servings: 4 servings
Course: Dinner
Cuisine: American
Calories: 850
Ingredients Equipment Method Notes

Ingredients
  

Caramelized Onions
  • 2 yellow onions thinly sliced
  • 2 tbsp unsalted butter
  • 1 tbsp olive oil
  • 1 tsp sugar
  • 0.5 tsp salt
  • 1 tbsp balsamic vinegar optional
Smash Burgers
  • 1.5 lb 80/20 ground beef
  • 1 tsp garlic powder
  • 1 tsp onion powder
  • salt and black pepper to taste
  • 4 brioche burger buns
  • 4 American cheese or cheddar, slices
  • 1 tbsp butter for toasting buns
Toppings
  • yellow mustard
  • dill pickle slices
  • shredded iceberg lettuce
  • sliced tomato

Equipment

  • 1 cast iron skillet

Method
 

Caramelize the onions
  1. Heat the unsalted butter and olive oil in a wide skillet over medium-low heat. Add the thinly sliced yellow onions, sugar, and salt, then stir to coat.
  2. Cook the onions, stirring every 5–7 minutes, for 35–45 minutes until deeply golden, jammy, and sweet. Keep the heat at medium-low so the onions caramelize without scorching.
  3. Add the balsamic vinegar in the last 5 minutes if using. Stir until absorbed, then set the onions aside.
Prep the smash burgers
  1. Divide the 80/20 ground beef into 6 oz loose balls, without overworking or packing them. Season lightly on all sides with garlic powder, onion powder, salt, and black pepper.
  2. Heat a cast iron skillet or flat griddle over high heat until just smoking. Arrange the surface so you can smash immediately once the balls hit the pan.
  3. Place one beef ball on the hot surface and immediately press down firmly with a flat spatula (or burger press) to smash it thin, about 1/4 inch thick. Press hard for 10 seconds.
  4. Season the top of the smashed patty with salt and black pepper. Let it cook undisturbed on the first side for 2–3 minutes until the edges are deeply browned and crispy and the top looks grey/cooked halfway up.
  5. Flip the patty so you see a deep-brown crust. Immediately lay American cheese on top and cook for 30–45 more seconds until the cheese is melted, then remove from the heat.
Toast buns and assemble
  1. Butter the cut sides of the brioche burger buns. Toast on the same skillet for 1–2 minutes until golden.
  2. Spread yellow mustard on the bottom bun and layer dill pickle slices on top. Add the smash patty with melted cheese, then pile on caramelized onions, followed by shredded iceberg lettuce and sliced tomato.
  3. Crown with the top bun and serve immediately. Repeat for the remaining patties so the crust stays crisp.

Notes

Pro tip: for the best crust, use just-smoking high heat and don’t move the patty during the first 2–3 minutes—leave it undisturbed until the edges are deeply browned. Store caramelized onions in the refrigerator up to 5 days (reheat gently in a skillet); cooked burgers reheat in a skillet for best texture within 2–3 days, and freezing is best avoided for assembled burgers. For a lighter option, use leaner ground beef (90/10) to reduce fat while keeping the smash technique and timing the same.