Prime Rib Sandwich Recipe

Prepare prime rib

If you have whole cooked prime rib: slice very thinly across the grain (1/8"–1/4"). If using leftover roast or store-sliced roast beef, separate into portions of about 8 oz per 2 sandwiches. Pat slices dry with paper towels.

Season

For Regular: lightly season the sliced beef with kosher salt and freshly ground black pepper. For Blackened: toss the slices in 2 tablespoons blackening spice blend to coat evenly. Heat 1 tablespoon olive oil in a heavy skillet over medium-high heat until shimmering; quickly sear blackened slices 20–40 seconds per side just to develop a dark crust without overcooking. Remove and rest briefly.

Combine mayonnaise, prepared horseradish, Dijon mustard, lemon juice, salt, and black pepper in a small bowl. Whisk until smooth and chill at least 10 minutes so flavors meld. Taste and adjust horseradish (more for heat) or salt.

Slice rolls in half. Spread butter thinly on cut sides. In a skillet over medium heat, add 1 tablespoon olive oil for onions; add thinly sliced onion and cook, stirring occasionally, until soft and caramelized (about 12–15 minutes). If you like a faster result, cook 8–10 minutes until softened and lightly browned.

Toast the buttered cut sides of the rolls in a separate skillet or under a broiler until golden (about 1–2 minutes) so they hold up to the meat and juices.

Spread about 3/4 tablespoon horseradish mayo on both the top and bottom interior of each roll (approximately 3 tablespoons total divided among 4 sandwiches).

Layer 4 ounces (about 1/2 cup by volume) of sliced prime rib on the bottom half of each roll. Top the meat with a portion of caramelized onions and a slice of provolone or Swiss cheese. If desired, add a lettuce leaf.

Place the sandwich under a broiler or in a hot skillet for 1–2 minutes just until the cheese melts and the sandwich is warmed through. For blackened option, do not overheat or you will cook the meat further.

Close sandwiches, press gently, slice in half and serve immediately with au jus for dipping if using.

Warm beef au jus or broth in a small saucepan over low heat. Stir in Worcestershire sauce and black pepper. Keep warm. Taste and adjust seasoning with salt or more Worcestershire if desired. Serve in small dipping bowls alongside sandwiches.