Wagyu French Onion Sliders Recipe

Prepare onions

Peel and thinly slice the yellow onion into uniform 1/8- to 1/4-inch slices so they cook evenly.

Cook onions low and slow

Heat 1 tbsp butter and 1 tbsp olive oil in a medium skillet over medium-low heat. Add the sliced onions and a pinch of salt (from the 0.5 tsp). Stir to coat and spread them into an even layer. Cook, stirring every 4–5 minutes, until soft and translucent (about 12–15 minutes).

Caramelize

Increase heat to medium, add the brown sugar (0.5 tsp) and continue cooking, stirring more frequently, until the onions turn deep golden brown and reduce significantly, about 10–15 more minutes. If they begin to stick or dry, add 1–2 tbsp water to deglaze and scrape up browned bits.

Finish with beef flavor and thyme

Add 2 tbsp beef stock and 1 tsp balsamic vinegar to the pan to deglaze and deepen flavor. Stir in 1 tsp chopped fresh thyme, 0.5 tsp salt, and 0.25 tsp black pepper. Cook another 1–2 minutes to meld flavors. Remove from heat and set aside until assembling sliders.

Whisk together 3 tbsp mayonnaise, 1 tsp finely chopped fresh thyme, 0.5 tsp lemon juice, and 0.5 tsp Dijon mustard in a small bowl. Season with 0.25 tsp salt and 1/8 tsp black pepper. Taste and adjust acidity or seasoning as needed. Refrigerate until assembly.

Form patties

Divide 10 oz wagyu ground beef into two equal portions (~5 oz each). Lightly form into 2 slightly wider-than-bun patties about 3/4-inch thick, being careful not to overwork the meat. Make a shallow thumb indentation in the center of each patty to prevent doming when cooking. Season both sides with 1 tsp kosher salt and 1/2 tsp freshly ground black pepper (divide between patties).

Cook patties

Heat a cast-iron skillet or heavy-bottom pan over medium-high heat until very hot. Add the patties and sear without moving for 2–3 minutes until a brown crust forms. Flip and cook another 2 minutes for medium-rare to medium (adjust time for desired doneness). During the last 30–45 seconds of cooking, place one slice of Havarti on each patty to melt; cover the pan briefly with a lid to help the cheese melt evenly.

Toast buns

While patties rest 2–3 minutes, halve the 2 brioche slider buns and spread a thin layer of the 1 tbsp softened butter on the cut sides. Toast buttered sides in a separate skillet or the residual heat of the meat pan for 1–2 minutes until golden and crisp.

Assemble

Spread a generous tablespoon of thyme mayo on the bottom half of each toasted brioche bun. Place the Havarti-topped wagyu patty on the mayo, then pile about half of the warm beefy caramelized onions over each patty (divide the onion mixture evenly). Add a sprig of fresh thyme on top if desired, then cap with the top bun.

Serve

Serve immediately while hot. Optionally pass extra thyme mayo and extra caramelized onions at the table.