King River Wagyu Burger Recipe

Form patties

Divide the 8 oz equivalent of Wagyu (0.5 lb) into two equal portions if making two smaller sliders or keep whole for one 8 oz patty. Gently form into a round patty about 3/4"–1" thick, pressing a slight dimple in the center to prevent doming. Handle as little as possible to preserve fat distribution.

Season both sides of the patty with 1 tsp fine sea salt and 1/2 tsp freshly ground black pepper, applying just before cooking to avoid drawing out moisture.

Heat a heavy skillet or cast-iron pan over medium-high heat until shimmering. Add 2 tbs neutral oil and swirl. Sear the patty 3–4 minutes per side for medium-rare (internal temp ~130–135°F / 54–57°C). For the last 30–45 seconds of the second side, place the aged cheddar slice on top and cover the pan to melt. Remove patty to rest on a warm plate for 3–5 minutes before assembling.

Heat a medium skillet over medium heat. Add 1 tbs unsalted butter and 1 tsp olive oil. When butter foams, add the thinly sliced onion (1 cup). Sprinkle 1/4 tsp salt and optional 1/4 tsp granulated sugar over the onions.

Cook, stirring every 2–3 minutes, lowering heat if browning too quickly, until onions turn deep golden brown and sweet, about 20–25 minutes. If they dry out, add a splash (1–2 tbs) water. Stir in 1 tsp balsamic vinegar at the end for brightness, cook 1 more minute, then remove from heat.

In a small bowl combine 1/4 cup mayonnaise, 1/2 tsp black truffle oil, 1/2 tsp Dijon mustard and 1/2 tsp fresh lemon juice. Season with 1/8 tsp salt and a pinch (1/16 tsp) black pepper. Whisk until smooth and taste; adjust truffle oil in 1/4 tsp increments if you want stronger aroma. Refrigerate until assembly.

Split brioche bun and butter cut sides with 1 tsp softened butter. Toast buttered sides in a dry skillet over medium heat until golden, about 1–2 minutes. Keep warm.

Soak

Place cut potatoes (2 cups) in a bowl and cover with cold water (about 500 ml). Soak 30 minutes to remove surface starch. Drain and rinse until water runs clear. Pat completely dry with kitchen towels.

First blanch (boil)

Bring a pot of salted water to a simmer with 1 tbs white vinegar. Add potatoes and simmer gently for 3–4 minutes until slightly tender at edges but not cooked through. Drain, spread on a tray, and refrigerate uncovered until dry and chilled, at least 30 minutes (can be done ahead).

First fry (low temp)

Heat vegetable oil in a deep pot to 275°F (135°C). Fry potatoes in batches for 4–6 minutes until pale and just beginning to set. Remove and drain on a rack. Let cool to room temperature; you can refrigerate to accelerate.

Second fry (crisping)

Increase oil temperature to 375°F (190°C). Fry potatoes for 2–3 minutes until golden and crisp. Remove and drain on paper or rack. Sprinkle with 1 tsp fine sea salt while hot, or reserve coarse salt for finishing as preferred.

Spread 1–2 tbs of black truffle dressing on the bottom bun. Place rested Wagyu patty with melted aged cheddar on top. Spoon 2–3 tbs caramelized onions over the cheese. Add optional lettuce or pickles. Top with the butter-toasted bun crown.

Serve burger with a generous portion of triple-cooked fries. Finish fries with a sprinkle of coarse sea salt (about 1/2 tsp) just before serving. Offer extra black truffle dressing on the side if desired.