French Dip Recipe

Prepare onions

Heat 1 tablespoon olive oil and 1 tablespoon butter in a medium skillet over medium heat. Add the thinly sliced onion, 1/2 teaspoon salt and 1/4 teaspoon black pepper. Sauté, stirring occasionally, until onions are soft and caramelized, about 18–22 minutes. Reduce heat to low to keep warm.

Warm prime rib

If prime rib is cold, warm it gently: add remaining 1 tablespoon butter to a clean skillet over medium-low heat. Add the thinly sliced prime rib in a single layer and heat for 1–2 minutes per side until just warmed through (avoid overcooking). Season lightly with a pinch of salt and pepper.

Assemble sandwiches

Preheat oven to 375°F (190°C). Split the baguette lengthwise and place both halves on a baking sheet, cut sides up. On each bottom half, layer half the warmed prime rib, top with half the caramelized onions, then arrange 4 slices of Swiss cheese over the meat and onions. Close sandwiches with the top halves of bread.

Melt cheese and toast bread

Brush the outside tops of the baguette with a thin smear of melted butter (optional). Place the assembled sandwiches in the oven and bake for 6–8 minutes, or until the cheese is melted and the bread is lightly toasted. For a crisper crust, broil 1–2 minutes watching carefully to avoid burning.

Slice and serve

Remove sandwiches from the oven and cut each baguette into 4 sandwich portions (about 3–4 inches each). Keep warm while preparing au jus or transfer to a serving platter. Serve each portion with a small bowl of hot au jus for dipping.

Combine base and aromatics: In a medium saucepan, combine 4 cups beef au jus or low-sodium beef broth, 1/4 cup dry red wine (if using), 1 tablespoon Worcestershire sauce, 1 teaspoon minced garlic and 1 teaspoon fresh thyme. Bring to a gentle simmer over medium heat.

Adjust seasoning: Taste and add 1/4 teaspoon salt and 1/4 teaspoon black pepper as needed. Maintain a low simmer for 4–5 minutes to meld flavors.

Thicken slightly (optional): If you prefer a slightly thicker dipping sauce, whisk 1 teaspoon cornstarch with 1 tablespoon cold water until smooth, then slowly whisk into the simmering jus. Cook 1–2 minutes until slightly thickened, then remove from heat.

Strain and serve: For a smooth au jus, strain the sauce through a fine-mesh sieve into a heatproof bowl or individual dipping cups. Keep warm until ready to serve alongside sandwiches.