Melt Recipe

Heat a wide skillet over medium heat. Add olive oil and butter. Once butter melts, add thinly sliced onion and stir to coat.

Sprinkle sugar and sea salt over onions. Cook, stirring every 3–5 minutes, lowering heat slightly if they start to brown too fast. Continue 20–30 minutes until deep golden and soft.

Toward the end, adjust heat to achieve even browning and stir in black pepper. Remove from heat and cool. Reserve 1/2 cup for the sandwich; store extras refrigerated.

Prepare bread

Spread 1 tablespoon of butter evenly on one face of each sourdough slice. These will be the exterior surfaces that contact the pan.

On the unbuttered side of one slice, spread the Dijon mustard evenly (about 1 tsp). This is the interior of the bottom slice.

Layer the cheeses: sprinkle half the cheddar (about 3/4 cup) across the mustard-spread slice, then add the Gruyère, then top with the remaining cheddar to create an even cheesy layer.

Arrange the roast beef in an even layer over the cheese. Avoid overstuffing so the sandwich closes flat.

Spoon 1/2 cup caramelized onions across the roast beef. If using fresh parsley, scatter over the onions now.

Top with the second slice of bread, buttered side out.

Heat a heavy skillet or cast-iron pan over medium-low heat. Place the sandwich in the pan and cook gently 3–5 minutes until the underside is golden brown and the cheese begins to melt.

Carefully flip the sandwich using a spatula. Cook the second side another 3–4 minutes. If the bread is browning before the cheese melts, lower the heat, cover the pan with a lid for 1–2 minutes to trap heat and finish melting.

Press the sandwich lightly with the spatula while cooking to encourage contact between cheese and bread. Remove to a cutting board when cheese is fully melted and both sides are golden.

Let rest 1 minute, then cut in half on a bias and serve immediately.

After removing the sandwich, reduce heat to medium-high and add demi-glace or reduced beef stock to the hot pan. Scrape up any browned bits left by the sandwich.

Whisk in butter, lemon juice, and coarse black pepper. Simmer 1–2 minutes until slightly glossy. Drizzle a tablespoon or two over the cut sandwich halves for an elevated serving.