French Onion Roast Beef Sandwiches
These cozy French Onion Roast Beef Sandwiches feature thin-sliced roast beef, golden caramelized onions, melted Gruyère cheese, and a garlicky thyme-kissed au jus for dipping. Baked hot and wrapped in foil, they’re crisp on the outside, gooey on the inside, and packed with rich, meaty flavor.
Ingredients
- 1 long French baguette
- 1 and 1/2 pounds 340g rare roast beef, thinly sliced
- 3 Tablespoons 42g unsalted butter
- 1 teaspoon fresh thyme leaves finely chopped
- 3 large yellow onions peeled and thinly sliced
- 1/2 teaspoon salt
- 1/2 teaspoon black pepper
- 1/4 teaspoon red pepper flakes
- 1/2 cup 113ml cooking sherry
- 2 cups 454ml beef stock
- 1/2 teaspoon cornstarch
- 1 teaspoon water
- 10 ounces Gruyère cheese grated
Instructions
- Slice baguette into 4 pieces, then cut each 3/4 through horizontally.
- Preheat oven to 500°F.
- Fill each piece with equal amounts of roast beef and place on foil.
- In a skillet, melt butter. Add thyme and onions. Cook for 20-25 minutes.
- Stir in salt, pepper, red pepper flakes. Add sherry. Cook 3-4 minutes.
- Pour in beef stock. Boil, then simmer 5 minutes.
- See full steps with tips & photos → https://wimpysdiner.net/french-onion-roast-beef-sandwiches/
Notes
- Make It Ahead: Caramelize onions up to 2 days in advance and store in the fridge.
- Cheese Swap: Swiss or provolone can be used if Gruyère isn’t available.
- No Sherry? A splash of white wine or a little extra broth can substitute in a pinch.
- More Crunch: Toast the baguette halves before filling for extra texture.