These French dip sandwiches combine thin-sliced deli roast beef, golden caramelized onions, mushrooms, and melted Muenster on toasted rolls with an easy-to-make beef jus on the side.
Heat the olive oil in a large skillet over medium heat. Add the sliced onion and minced garlic. Sauté for 2 to 3 minutes, until the onion softens.
Add the mushrooms, a pinch of salt, and a few grinds of black pepper. Cook, stirring often, until the mushrooms release their moisture and start to brown, about 5 to 6 minutes.
Stir in the Worcestershire sauce and continue cooking for another 4 to 5 minutes, until the onions are lightly caramelized.
While the vegetables cook, preheat the oven to 375°F. Slice the hoagie rolls lengthwise, spread them open, and arrange on a baking sheet. Line each with 2 slices of Muenster cheese.
Bake for 5 minutes, or until the cheese is melted and the rolls are lightly toasted.
Pour the beef broth into the skillet with the onion-mushroom mixture. Bring to a simmer and cook for 5 minutes.
Using a slotted spoon, transfer the onions and mushrooms to a fine mesh strainer set over a bowl. Let them drain.
Remove the pan from the heat. Using tongs, add the roast beef to the broth and stir gently to coat the slices with jus (see notes).
Fill each toasted roll with a portion of the onion-mushroom mixture, then use tongs to add a portion of warmed roast beef on top.
Divide the remaining broth among 4 small bowls and serve the sandwiches hot with jus for dipping.
Notes
WARMING THE ROAST BEEF: Add the roast beef to the broth a slice at a time so they warm evenly and don't stick together. Depending on the diameter of your pan, you may want to warm the beef in two batches.