French Dip Recipe

Prepare au jus

Place beef bones (if using) and 4 cups beef broth in a medium saucepan or small stockpot. Add smashed garlic, thyme, bay leaf, Worcestershire sauce, salt, and pepper. Bring to a simmer over medium heat, then reduce to low and simmer gently, uncovered, 20–25 minutes to concentrate flavors. If using wine, add it after the initial simmer and reduce by half before adding additional stock.

Strain the liquid through a fine mesh sieve into a clean saucepan or bowl, pressing solids to extract juices. Discard solids (or reserve bones). If the jus seems thin, return to saucepan and simmer until reduced to about 2 to 2 1/2 cups. Taste and adjust seasoning with additional Worcestershire or salt and pepper. Keep warm over the lowest heat or transfer to a small slow cooker/thermos for serving.

Warm and slice roast beef

If your Angus roast beef is cold, warm it gently: place slices on a rimmed baking sheet, cover loosely with foil, and warm in a 300°F (150°C) oven for 6–8 minutes until just warmed through (do not overcook). Alternatively, briefly dip slices in simmering au jus to heat. Keep warm until assembly.

Heat olive oil and 1 tbsp butter in a large skillet over medium-low heat. Add thinly sliced onions and sprinkle with 1 tsp sugar and 1 tsp salt. Stir to coat and spread into an even layer.

Cook slowly, stirring every 3–5 minutes. After 15–20 minutes the onions will soften and begin to brown at the edges. If they are sticking, add a tablespoon of water to deglaze. Continue cooking 10–15 more minutes until deep golden brown and sweet, about 25–35 minutes total.

Stir in 1 tsp balsamic vinegar (optional) in the final minute to brighten flavor. Adjust salt to taste. Remove from heat and keep warm.

In a small bowl, combine 1 cup mayonnaise, 2 tsp prepared horseradish, 1 tsp lemon juice, 1 tsp Dijon, 1/2 tsp minced garlic, 1/2 tsp kosher salt, and 1/4 tsp black pepper. Mix until smooth and taste; add more horseradish for heat or lemon for brightness. Refrigerate until ready to assemble.

Preheat broiler or oven to 425°F (220°C) if you prefer to melt cheese under direct heat. Split the baguette lengthwise and spread softened butter on cut sides. Place buttered cut sides down on a baking sheet and toast under broiler or in oven for 2–4 minutes until lightly golden (watch carefully to avoid burning).

Spread a generous layer of horseradish aioli on both cut sides of the toasted baguette. Layer warm roast beef slices evenly on the bottom half, allowing meat to slightly overlap. Top beef with caramelized onions, then arrange Swiss cheese slices over the onions and beef.

Place assembled sandwich under broiler or back in the oven at 425°F (220°C) for 1–3 minutes just until cheese melts and bubbles. Remove from oven.

Close sandwich with top half of baguette, press gently, and slice into 4 portions. Garnish with chopped parsley if desired. Serve immediately with individual bowls of hot au jus for dipping.