Aaa Prime Rib Sandwich Recipe

Prep Prime Rib

If using refrigerated leftover prime rib, let it sit at room temperature for 15–20 minutes. Gently reheat slices in a low oven (120°C / 250°F) on a tray covered with foil for 8–12 minutes until warm but not overcooked. Alternatively, warm in a skillet with a splash of beef broth for 2–3 minutes. Season lightly with 1 tsp kosher salt and 1/2 tsp freshly ground black pepper while warming.

Prepare Baguette

Preheat oven to 200°C / 400°F (or use a hot skillet). Split the demi baguette lengthwise. Spread softened butter evenly on cut sides. Place cut-side up on a sheet tray and toast in the oven 5–7 minutes until golden and crisp, or toast in a skillet over medium heat 2–3 minutes per side.

Assemble Sandwich

Spread 1–2 tablespoons of horseradish aioli on both cut sides of the toasted baguette. Layer warmed shaved prime rib evenly across the bottom half, then top with sliced cheese. Place the top half of the baguette and press gently to compact the sandwich slightly. If you prefer melted cheese, return the assembled open sandwich to the oven or under a broiler for 1–2 minutes until cheese softens—watch carefully to avoid burning.

In a small bowl, whisk together 1/2 cup mayonnaise, 3 tsp prepared horseradish, 1 tsp Dijon mustard, 1 tsp lemon juice and 1/2 tsp grated garlic until smooth. Season with 1/4 tsp salt and 1/8 tsp black pepper. Taste and adjust horseradish for desired heat. Refrigerate until assembly. Makes enough to smear on the sandwich and to serve extra on the side.

Slice and Dry

Separate the very thin onion slices into individual rings/strings and pat dry with paper towels to remove surface moisture. This helps achieve maximum crispness.

Dredge

In a wide bowl combine 3/4 cup all-purpose flour, 2 tsp cornstarch, 1/2 tsp paprika and 1/2 tsp salt. Toss the onion strings in the flour mixture until well coated. Shake off excess flour.

Fry

Heat vegetable oil in a heavy-bottomed pot or fryer to 175°C / 350°F (use an oil thermometer). Fry the coated onion strings in small batches for 1.5–2.5 minutes until golden brown and crisp. Remove with a slotted spoon to a paper towel-lined tray and season immediately with a pinch of salt. Keep warm in a low oven (100°C / 210°F) while frying remaining batches.

Combine 1 cup beef demi-glace and 1/2 cup beef broth in a small saucepan over medium heat. Add 1 tsp Worcestershire sauce and optional 1 tablespoon red wine. Bring just to a gentle simmer, reduce heat and simmer 3–5 minutes to meld flavors. Whisk in 1 teaspoon unsalted butter for sheen and add 1/4 tsp freshly ground black pepper. Taste and adjust seasoning. Keep warm and serve in a small bowl or cup alongside the sandwich for dipping.

Place the assembled sandwich on a cutting board. Pile a generous handful of crispy onion strings on top of the cheese layer (or serve them on the side if preferred). Slice the sandwich into 2 portions crosswise. Serve immediately with a small cup of hot au jus for dipping and additional horseradish aioli on the side.