The Rumba Melt Recipe

Prep onions

Peel and thinly slice half a yellow onion into half-moon slices about 1/8" thick so they cook evenly.

Heat a 10" skillet over medium heat. Add 1 tablespoon olive oil and 1 teaspoon unsalted butter. When the butter foams, add the sliced onions and toss to coat.

Season the onions with 1/4 teaspoon kosher salt and the optional 1/2 teaspoon light brown sugar. Cook, stirring every 2–3 minutes, until soft and beginning to brown, about 10–12 minutes. Reduce heat to medium-low if they start to burn.

When onions are deeply softened and lightly caramelized (about 12–18 minutes total depending on heat), deglaze the pan with 1/2 teaspoon sherry vinegar. Stir to lift any browned bits, cook 30 seconds more, then remove onions to a bowl and keep warm.

Form a single beef patty (about 5–6 oz) if not pre-formed; press a shallow dimple in the center to reduce puffing. Season both sides with 1/2 teaspoon salt and 1/4 teaspoon black pepper.

Heat a cast-iron skillet or griddle over medium-high heat until hot. Add the patty and cook undisturbed for 3–4 minutes to develop a crust.

Flip the patty and immediately top with the sliced Gruyère (2 oz). Reduce heat to medium-low, cover the pan with a lid or tent with foil to melt the cheese, and cook an additional 3–4 minutes for medium doneness (adjust time for desired doneness).

While the cheese melts, spread 1 tablespoon room-temperature unsalted butter evenly on one side of each slice of marble rye. Place buttered-side down on a separate clean skillet or griddle over medium heat and toast until golden brown, about 1–2 minutes per side. If using the same pan, toast briefly after removing the patty, wiping excess grease if necessary.

If desired, spread 1/2 teaspoon Dijon mustard on the untoasted side of one slice of rye.

Assemble the sandwich: place the melted-Gruyère-topped patty on one slice of toasted marble rye, pile the warm sautéed onions on top of the cheese, and close with the second slice of rye, buttered side out.

Press gently, slice in half if desired, and serve immediately while hot.