A toasted French Dip Sandwich with melted Gruyère and a delicious homemade Au Jus is easy to make with leftover prime rib roast or deli meat! Thinly sliced beef is soaked in the Au Jus, then placed on a buttered toasted roll and topped with grated cheese and broiled in the oven. Absolutely delicious!

Why this recipe is so great:

Fantastic use of leftover roast: If you've recently made a beef roast and you happen to have leftovers, you might be wondering how to use them. These sandwiches not only taste great, but they are easy to make and are one of the best ways to serve leftover roast. I've made these French Dip Sandwiches with my leftover Smoked Prime Rib but have also made them with my oven roasted prime rib roast.
Works with sliced deli meat: Craving a French Dip Sandwich but don't have leftover sliced roast? No problem! Head to the deli and have them slice you some.
Homemade Au Jus: Real Au Jus is just the cooking liquid created when braising, or slow cooking, meat. You can't enjoy a French Dip without Au Jus to dip it in, so you have two choices - buy the packet at the store or make homemade Au Jus. Not gonna lie; the Au Jus made from a packet tastes great, but if you take the time to look at the ingredients you'll want to make your own.

Ingredients needed:

Exact quantities are listed in the recipe card below, but here is a summary.

Roast beef: Can be from the deli or leftover from a home-cooked roast. For best results, thinly slice the meat.
French rolls: These are found in the bread department of any major grocery store near the buns.
Butter: I always recommend a high quality butter like Kerrygold.
Gruyère cheese: One of the best melting cheese and the flavor is fantastic on a French Dip Sandwich.
Au Jus: Homemade is always best, but you can also make from a packet.

For an extra kick, you can also make Horseradish Sauce to spread onto the sandwiches.

How to make French Dip Sandwiches:

Detailed step by step instructions are listed in the recipe card below, but here is a summary.

Warm the meat: The trick with leftover prime rib is to warm the meat without cooking it. Simply have the Au Jus warming on the stove and add the thinly sliced meat. Maintain a temperature just below a simmer and only soak the meat as long as it takes to warm it.
Toast the rolls: For the best flavor and also to prevent the bread from instantly getting soggy in the dipping Au Jus, cover it with a thin layer of butter and toast under the broiler.
Add beef and cheese to rolls: Using tongs, pull the warmed sliced beef from the Au Jus, shake off any excess liquid, and add it to the rolls. Top the sliced roast beef with the grated Gruyere.
Broil: Set the open-faced sandwiches under the broiler and heat until the cheese has melted.

Serve warm with individual portions of the Au Jus!

sliced beef warming in Au Jus — warm sliced beef in Au Jus

toasted French rolls with butter — warm sliced beef in Au Jus

Recipe tips for perfect results:

Thinly slice meat: These sandwiches are the most enjoyable when the meat is thinly sliced. Prime rib really does create the most mouthwatering sandwich because the meat is so tender and flavorful.
Toast the bread well: If the bread isn't toasted well prior to making the sandwiches, it will fall apart. Be sure not to skip this step.