Heat a medium skillet over medium heat. Add butter and olive oil. Add the thinly sliced onion and a pinch of salt. Cook, stirring occasionally, until softened, about 6–8 minutes.

Caramelize

Reduce heat to medium-low, add sugar, and continue to cook, stirring every few minutes, until onions turn deep golden brown and jammy, about 20–25 minutes. If onions begin to stick, add a tablespoon of water to deglaze. Remove from heat and set aside; measure 1/2 cup for the burger.

Dressing

In a small bowl, combine mayonnaise, ketchup, yellow mustard, pickle juice, onion powder, salt, and black pepper. Whisk until smooth. Taste and adjust seasoning. Refrigerate until assembly.

Buns & Toppings

Cook the bacon in a skillet over medium heat until crisp, about 6–8 minutes, turning once. Transfer to a paper towel-lined plate to drain. Keep warm.

Lightly butter the cut sides of the hamburger bun and toast them on a griddle or skillet over medium heat until golden, about 1–2 minutes. Set toasted buns aside, cut sides up.

If using store-bought caramelized onions, skip the onion-making steps and have 1/2 cup ready. Slice pickles and prepare cheddar slices.

Beef Patties

Portion meat

Divide 250 g of 80/20 ground beef into two equal balls (~125 g each) if you prefer two thin patties stacked, or leave as one 250 g ball for a thicker single patty. For a classic smash burger, work with one ball at a time (about 125 g).

Preheat griddle

Heat a heavy cast-iron skillet or flat griddle over high heat until very hot. Add 1 tsp neutral oil and spread to coat.

Smash

Place a ball of beef on the hot surface. Using a sturdy spatula (and optionally a second spatula or a burger press), press the ball flat immediately to about 1/4-inch (6 mm) thickness. Hold pressure for 10–15 seconds to create maximum contact and a crisp edge.

Season & cook

Season the exposed top with a generous pinch of kosher salt and a little black pepper. Cook undisturbed for 2–3 minutes until the edges are deeply browned and juices appear on top.

Flip & cheese

Using a thin spatula, scrape under the patty and flip. Immediately place a slice of cheddar on the hot patty so it melts while the second side cooks, about 30–60 seconds.

Repeat

Repeat with the second ball if making two patties. For a double burger, stack the two finished patties while assembling.

Assembly

Spread 1–1.5 tablespoons of dressing on the bottom bun.

Place the hot patty (or patties) directly on the dressed bottom bun.

Top with caramelized onions (about 2–3 tablespoons), a slice of crispy bacon (or two halves), and pickles. Add lettuce if using.

Spread a thin layer of dressing on the top bun and place it on top. Press gently to compact.

Serve immediately with fries or a side of your choice.