French Dip Recipe

Prepare the beef

If your prime rib is not already cooked and thinly sliced, cook or reheat a roast to medium-rare (internal 125–130°F for carryover to 135°F). Let rest at least 15 minutes, then slice as thinly as possible across the grain (about 1/8"–1/4" thick). You should have about 1 pound of sliced beef.

Season the beef

Lightly toss or sprinkle the sliced beef with 1/2 tsp kosher salt and 1/4 tsp freshly ground black pepper to taste. Set aside while you prepare the rolls and au jus.

Make Parmesan butter and toast rolls

Preheat oven broiler to high (or oven to 425°F). In a small bowl, melt 4 tbs unsalted butter. Stir in 2 tbs grated Parmesan. Split the 4 hoagie rolls lengthwise (do not separate halves). Brush the cut sides evenly with the Parmesan butter. Place cut side up under the broiler or in the oven for 2–3 minutes until golden and crisp — watch carefully to avoid burning.

Assemble sandwiches

Spread about 1/2 tsp Dijon mustard (if using) on the bottom halves of each toasted roll. Pile ~4 oz (1/4 lb) of thinly sliced prime rib onto each bottom half. Top the beef with 2 slices of Swiss cheese per sandwich (arrange to cover). Place the filled sandwiches on a baking sheet and warm in a 350°F oven for 5–7 minutes, or until the cheese is melted and the beef is warmed through. Close sandwiches with the toasted top half and keep warm, covered loosely with foil, until serving.

Sauté aromatics

In a medium saucepan over medium heat, add 1 tbs beef drippings or unsalted butter. When hot, add the sliced half onion and smashed garlic cloves. Cook, stirring occasionally, until softened and lightly browned, about 4–6 minutes.

Deglaze and simmer

Add 1/4 cup dry red wine (if using) to deglaze the pan, scraping up browned bits. Let it reduce about 1–2 minutes. Add 3 cups beef broth, 1 tsp Worcestershire sauce, 1 tsp soy sauce, 1 thyme sprig, and 1 bay leaf. Bring to a gentle simmer and cook 10–12 minutes to meld flavors.

Season and finish

Taste the jus and add 1/4 tsp salt and 1/4 tsp freshly ground black pepper as needed. Remove and discard the thyme sprig, bay leaf, garlic and onion (or leave them in for rustic presentation). If you prefer a slightly thicker jus, whisk 1 tsp cornstarch with 1 tbs cold water to form a slurry and slowly whisk into the simmering jus; cook 1–2 minutes until slightly thickened. Keep hot until serving.

Optional enhancement with roast drippings

If you have drippings from the cooked prime rib, stir 1–2 tbs strained drippings into the finished jus for a richer flavor before serving.

Place each melted-Swiss prime rib sandwich on a plate and serve immediately with a small bowl or cup of hot au jus for dipping. Encourage diners to dip each bite or half-sandwich into the jus.