French sandwich with beef and broth

Ingredients:

• 6 French rolls
• 900 g of beef from the upper thigh
• 1 small onion, coarsely chopped
• 1 small carrot, coarsely chopped
• 1 stalk celery, coarsely chopped
• 1 small leek, white and light green parts only, coarsely chopped
• 2 cloves garlic, chopped
• 1 sprig of fresh thyme
• 1/4 tsp dried sage
• 1/4 teaspoon dried oregano
• 1/4 tsp ground nutmeg
• 1/2 tsp ground cloves
• 1/2 tsp ground allspice
• 2 cups rich chicken broth
• Mustard sauce, for serving

Preparation:

1. Preheat oven to 150°C.
   
   Combine chopped vegetables, garlic, and thyme in a large roasting pan. Rub the beef with dried herbs and spices. Season generously with salt and pepper. Place the beef, fat side up, on the vegetables and roast until a thermometer inserted into the thickest part of the meat registers 135 degrees Fahrenheit (54 degrees Celsius), about 45 minutes. Remove the beef from the pan, cover loosely with foil, and let it rest for 30 minutes.
2. While the meat is cooling, place the roasting pan on the stove and cook the vegetables over high heat until they are browned (but not burnt) and the liquid has evaporated. Drain off any excess fat.
   
   Add the broth to the pan, scraping up any browned bits with a wooden spoon. Transfer the liquid and vegetables to a medium saucepan and bring to a boil. Reduce the heat to low and simmer until the liquid is reduced by half, about 30 minutes. Strain the sauce and season with salt and pepper. Keep warm.
3. Trim excess fat from the beef and cut it into thin slices. Cut the buns in half horizontally. Heat them in the oven. Dip the bottom half of each bun into the sauce. Place a small amount of beef on top. Dip the cut side of the top halves of the buns into the sauce and cover the meat with them. Serve with mustard sauce.