Smash Burger Recipe

Prepare the zucchini: thinly slice the zucchini lengthwise into 1/8–1/4-inch slices or into coins so pieces are uniform.

Make pickling brine: in a small saucepan combine white vinegar, water, sugar, kosher salt, mustard seeds, and red pepper flakes. Warm over medium heat, stirring, just until sugar and salt dissolve; do not boil.

Pickle: place zucchini slices in a heatproof jar or bowl and pour the warm brine over them to fully submerge. Let cool to room temperature, then cover and refrigerate for at least 30 minutes (preferably 1–2 hours) before assembling. These keep well for 3–5 days refrigerated.

Heat a skillet over medium-low heat and add the olive oil and 1 tsp butter. Add the thinly sliced onion and spread into an even layer.

Season with 1/4 tsp kosher salt and the optional 1/4 tsp sugar. Cook slowly, stirring or scraping every 2–3 minutes so they brown evenly. Reduce heat if they start to burn. Continue for 18–25 minutes until deep golden brown and very soft.

Finish: stir in sherry vinegar or a splash of balsamic (1/2 tsp) to deglaze the pan and brighten flavor. Remove from heat and set aside until assembly.

Divide the meat: portion the 1 lb ground beef into four loose balls (~4 oz each) for two double smash patties (two balls per burger). Do not overwork the meat; gently form into loose rounds.

Preheat Cook Surface

Heat a heavy cast-iron skillet or griddle over high heat until very hot (a drop of water should sizzle and evaporate immediately). Add 2 tbs neutral oil and spread to coat.

Smash and sear: working one ball at a time, place the beef ball on the hot skillet and immediately press down firmly with a heavy spatula or a second flat pan to create a thin patty (~1/4 inch). Hold pressure for 8–12 seconds to maintain shape. Season the exposed side with a pinch of salt and ground pepper.

Cook first side until deeply browned and crisp at the edges, about 2–3 minutes. Flip and immediately season the second side with salt and pepper.

Add cheese & finish: after flipping, top each patty with the fontina (about 1.5 oz per patty if making four) and cover the skillet or place a lid to help cheese melt, about 30–45 seconds. If using butter for finishing, add 1/2 tbs butter to the pan and spoon the melted butter and juices over the patties before removing.

Repeat for remaining meat. For a double burger, stack two cheese-topped patties on each bun bottom.

Toast buns: spread 1 tbs softened butter across cut sides of the buns. In a clean skillet over medium heat, toast buttered sides until golden brown, about 1–2 minutes.

Spread condiments: mix mayonnaise and mustard (2 tbs mayo + 1 tsp mustard) and spread evenly on the toasted bun tops or bottoms according to preference.

Assemble burgers: place mayonnaise-coated bottom bun, add a stack of one or two fontina-topped smash patties (depending on desired size), top with a generous spoonful of caramelized onions, then 3–4 slices of the zucchini pickles, and finish with the bun top.

Serve immediately while patties are hot and cheese is melty.