Hot Roast Beef Sandwich With Onion Jam Recipe

Prepare onions

Peel and thinly slice enough yellow onions to yield about 3 cups (approximately 2 medium-large onions).

Cook onions slowly

Heat 2 tbs butter and 1 tbs olive oil in a large skillet over medium-low heat. Add the sliced onions and a pinch of salt. Cook, stirring every few minutes, until soft and beginning to brown, about 20–25 minutes. Lower heat if they start to crisp too quickly.

Caramelize and flavor

When the onions are deeply softened and golden (after 20–30 minutes total), sprinkle 2 tbs brown sugar over them and stir to dissolve. Add 2 tbs balsamic vinegar, 1 tbs beef or chicken stock, and 1 tsp fresh thyme leaves. Continue to cook 3–5 minutes until liquid reduces to a jammy consistency. Taste and season with 1 tsp salt and 1 tsp black pepper, adjusting to preference. Remove from heat and set aside; the jam will thicken as it cools.

Prepare rolls

Preheat oven broiler (or set oven to 425°F / 220°C for a quick toast). Split 4 garlic rolls horizontally. Melt 2 tbs butter and brush cut sides lightly. Optionally rub the cut surface with 1 garlic clove for a subtle garlic note. Place rolls cut-side-up on a baking sheet.

Toast rolls

Broil (or bake) rolls until edges are golden, about 2–4 minutes under a broiler or 5–7 minutes at 425°F. Watch carefully to avoid burning. Remove from oven.

Warm roast beef

While rolls toast, warm 12 oz shaved roast beef in a skillet over medium-low heat with a few tablespoons of the warmed beef au jus or broth so meat is heated but not dried out, about 2–3 minutes. Season lightly with 1/2 tsp salt and 1/2 tsp black pepper if needed. Keep the au jus warm in a small saucepan for serving.

Assemble sandwiches

Place the toasted bottom halves of the rolls on the baking sheet. Spread a generous tablespoon of onion jam on each bottom roll. Pile about 3 oz warmed shaved roast beef onto each roll (divide 12 oz evenly among 4 sandwiches). Spoon any pan juices from the warmed beef over the meat for extra moisture and flavor.

Add cheese and melt

Top the roast beef with 2 oz fresh mozzarella per sandwich (sliced or shredded). Place the baking sheet under the broiler for 1–2 minutes, or return to 425°F oven briefly, until the mozzarella melts and just begins to bubble. Remove from oven.

Finish

Place the top roll on each sandwich. If desired, brush the top with a little melted butter and sprinkle with chopped parsley or red pepper flakes. Serve immediately with warmed beef au jus in small bowls or cups for dipping.

Provide small ramekins of the warmed au jus for dipping. Garnish sandwiches with chopped parsley and a light dusting of red pepper flakes if using. Serve hot.