Impress your guests with Smashburgers with Special Truffle Sauce—thin, crispy patties layered with nutty Gruyère, peppery baby arugula, and sweet caramelized onions. This elevated take on a fast-food favorite delivers big flavor while staying straightforward to prepare. Make the truffle sauce and caramelized onions ahead of time for an easy, stress-free meal when entertaining.
The signature component is a homemade truffle sauce made from mayonnaise, Dijon mustard, finely chopped cornichons, lemon juice, and a touch of black truffle oil. A little truffle oil goes a long way—its earthy, umami note lifts these burgers without overpowering them. For the patties, use 85/15 ground beef for a good balance of fat and flavor; when smashed thin on a hot cast-iron surface, these become deeply caramelized at the edges while staying juicy in the center. Gruyère is my top choice for cheese thanks to its sharp, nutty profile, though Swiss or white cheddar are excellent alternatives.
Ingredients
- Special Truffle Sauce: 1/2 cup mayonnaise, 1/4 cup finely chopped cornichons, 1 tbsp Dijon mustard, 1 tbsp freshly squeezed lemon juice, 1 tbsp black truffle oil, kosher salt and freshly ground black pepper to taste
- Caramelized Onions: 1–2 tbsp extra-virgin olive oil, 2 yellow onions thinly sliced, pinch of kosher salt
- Burgers: 2 lb ground beef (85/15), kosher salt and freshly ground black pepper to taste, unsalted butter (optional for toasting)
- For Assembly: 6 brioche buns, 12 slices Gruyère (or Swiss/white cheddar), baby arugula, cornichons for garnish
Step-by-step
Step one: make the truffle sauce
In a small bowl, whisk together mayonnaise, finely chopped cornichons, Dijon mustard, lemon juice, and black truffle oil. Season with kosher salt and freshly ground black pepper to taste. Cover and refrigerate—this sauce improves if made a few hours ahead and will keep in an airtight container for up to five days.
Step two: make the caramelized onions
Heat 1 to 2 tablespoons of extra-virgin olive oil in a large skillet over medium heat. Add the thinly sliced yellow onions with a pinch of kosher salt. Cook, stirring frequently, for 30 to 40 minutes until they are deeply golden and sweet. If the onions begin to brown too quickly, reduce the heat. When finished, set aside until assembly.
Step three: form and cook the burgers
Divide the ground beef into 12 equal portions (about 2½ to 3 ounces each) and roll each portion into a loose ball—avoid overworking the meat. Heat a large cast-iron skillet or griddle over medium-high heat until very hot. Working in batches, place 2 to 3 meatballs on the surface and immediately smash each down with a heavy spatula or burger press until very thin. Season lightly with salt and pepper.
Cook the smashed patties for 2 to 3 minutes, until the edges are crisp and browned. Flip, immediately top each patty with a slice of Gruyère, and cook another 1 to 2 minutes until the cheese melts and the patty is cooked through. Transfer finished patties to a plate and repeat with remaining meatballs.
Step four: toast the buns
Optionally spread a little unsalted butter on the cut sides of brioche buns, then toast them cut-side down in the skillet until golden and fragrant.
Step five: assemble the burgers
Spread a generous spoonful of truffle sauce on each bottom bun. Add a handful of baby arugula, stack two cheesy smash patties, and top with a spoonful of caramelized onions. Close with the bun top and secure with a cornichon and toothpick if desired. Repeat for all burgers and serve immediately while hot and melty.
Recipe FAQs
Yes. The truffle sauce can be prepared up to five days ahead and stored in an airtight container in the refrigerator. Caramelized onions also keep well for several days and can be reheated gently before assembling the burgers.
What makes a burger a smashburger?
Smashburgers are formed by pressing small meat portions very thin on a hot griddle or cast-iron pan. That immediate contact produces crispy, deeply browned edges and an intensified beef flavor. They’re typically cooked quickly and often served stacked with cheese and toppings.
Servings: 6 (makes 12 thin patties, two per burger). For best results use 85/15 ground beef and a high-quality black truffle oil—just a tablespoon in the sauce is enough to add that distinctive, earthy note.
Next time you crave a juicy, flavorful burger, try these Smashburgers with Special Truffle Sauce. They’re easy to scale for a crowd, make-ahead friendly, and offer an elevated, restaurant-worthy bite at home—crispy edges, melty Gruyère, peppery arugula, and a memorable truffle finish.
Photography and styling credit: Eat Love Eats.