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Simple Onion Smash Burgers

Delicious Simple Onion Smash Burgers recipe with step-by-step instructions.
Print Recipe
Prep Time 10 minutes
Cook Time 20 minutes
Total Time 30 minutes
Servings 4 burgers
Calories 3650 kcal

Ingredients
  

For the burger sauce:

  • 1/2 cup mayo (I prefer Hellmann's mayonnaise)
  • 2 tbsp sour cream
  • 1.5 tbsp mustard
  • 1 tsp worcestershire sauce (Lea & Perrins brand provides the best depth)
  • 1/2 tsp garlic powder
  • 1/2 tsp pepper
  • 1/4 tsp smoked paprika
  • 1/2 tsp granulated sugar

For the burgers:

  • 2.2 lb ground beef (80/20 ratio for maximum juiciness)
  • 2 large onions (shaved into paper-thin slices with a mandoline)
  • 8 slices sharp cheddar cheese
  • 4 large Brioche buns (I like St Pierre for this)
  • 1 tsp kosher salt
  • 1/2 tsp freshly ground black pepper
  • 3 tbsp Kerrygold unsalted butter

Instructions
 

  • Whisk together the mayo, sour cream, mustard, worcestershire sauce, garlic powder, pepper, smoked paprika, and granulated sugar in a bowl until smooth and well combined. Set aside at room temperature. While the sauce rests, use a mandoline to shave the onions into paper-thin slices—this is crucial for the smashing technique, as thin onions will caramelize quickly and create that signature crust. Divide the ground beef into 8 equal portions and gently form them into balls without overworking the meat; this helps maintain the beefy texture when smashed.
  • Heat your grill to medium-high heat (around 375-400°F if using a thermometer). Place one beef ball directly on the hot grill grate, then immediately top it with a generous handful of shaved onions and a pinch of kosher salt. Using a sturdy spatula, press down firmly on the onions and beef, smashing them together until the patty is very thin and the onions begin to adhere to the meat. This creates the beloved crispy, caramelized crust that defines smash burgers. Cook without moving for 2-3 minutes until deeply browned, then flip the patty carefully using your spatula.
  • After flipping, cook the second side for 1-2 minutes until golden brown. I like to add the cheese while the patty is still on the grill so it melts slightly from the residual heat—it creates better adhesion when stacking. Top with one slice of sharp cheddar and remove from the grill. Repeat Steps 2 and 3 with the remaining 7 beef balls, working in batches as your grill space allows, until all 8 patties are cooked with cheese melted on top.
  • Pair up the cooked patties by placing two cheese-side-in onto each other, creating 4 double-stacked burgers with the melted cheese acting as the glue. While the patties rest, butter both sides of each brioche bun and place them cut-side down on the grill for 1-2 minutes until golden and lightly charred. This adds a textural contrast and prevents the buns from becoming soggy.
  • Spread a generous dollop of the special sauce from Step 1 on the bottom half of each toasted bun, then place one double-stacked patty on top. Add another light smear of sauce on the top bun and set it in place. Serve immediately while everything is still warm and the cheese is fully melted.