Melt butter in a large skillet over medium heat. As soon as the butter melts, stir in the chopped shallots. Cook for about 3 minutes, until they begin to soften.
2 Tablespoons butter, 1 medium shallot
Stir in the flour and cook for about 1 minute more, then whisk in the wine, sherry, or vermouth, if using. Let this liquid bubble off, then slowly pour in the beef broth, whisking as you go.
1 Tablespoon all-purpose flour, 2 Tablespoons dry white wine, dry sherry, or vermouth, 2 cups low-sodium beef broth or bone broth
Once all of the broth is added, increase heat to medium-high to bring the mixture to a boil. Reduce heat back to medium-low, and let it simmer gently while you prep the rolls and roast beef. This is your au jus.
Split open and lightly toast the rolls, if desired, in a 250° F oven, or in a toaster oven.
6 sandwich rolls
Spread the slices of roast beef across a large, microwave-safe plate. Sprinkle the steak seasoning blend generously on top, and warm on 50% power in the microwave for about 1 minute, just until lightly warmed. (If you prefer not to use the microwave, you can dredge the meat in the sauce on the skillet, or warm it lightly on a baking sheet in the oven at 250° F.)
1 and 1/2 pounds thinly-sliced deli roast beef, 1-2 Tablespoons Montreal Steak seasoning blend
To assemble sandwiches, fill each roll generously with the seasoned roast beef and a slice of cheese, if desired. Pour the au jus into 4-6 small bowls or ramekins and serve as a dipping sauce along with the sandwiches. Enjoy warm!
Swiss or provolone cheese