This keto French dip casserole has everything you love about the classic sandwich, minus the roll. Thin slices of roast beef mingle with sweet caramelized onions under a thick layer of melted provolone or Swiss. Then you dip each forkful into warm beef broth, just like au jus at a deli.

It takes about 15 minutes of prep and a little under an hour from start to finish. It makes 4 servings and fits nicely into a low-carb or keto week, since there is no bread, flour, or sugar in the dish.

Why This French Dip Casserole Works

The flavor of a good French dip comes from three things: tender beef, sweet onions, and salty broth. This casserole keeps all three. Cooking the onions slowly in butter for 10 to 12 minutes brings out their natural sweetness, which balances the rich beef and cheese.

Because the roast beef is already cooked, it only needs to warm through. That keeps it tender instead of chewy. The cheese melts into a golden top that holds the casserole together, so you can cut it into neat squares.

Ingredients and Easy Swaps

• Sliced roast beef (1 1/2 pounds): Deli roast beef works great. Ask the counter to slice it a little thicker than sandwich thin. Leftover pot roast is another good option.
• Ground beef option: If you use ground beef, brown it fully in the skillet to 160°F and drain the fat before adding the garlic powder.
• Onion (1 large): Yellow onions caramelize best. Sweet onions also work.
• Provolone or Swiss (2 cups shredded): Provolone is mild and stretchy. Swiss adds a nutty flavor. A mix of both is great.
• Beef broth (1 1/2 cups): This becomes your dipping sauce. Use a good-quality broth or bone broth for the best taste.
• Butter or olive oil, garlic powder, salt, and pepper: Simple seasonings that let the beef shine.

How to Make It at a Glance

1. Heat the oven to 375°F.
2. Melt butter in a skillet and cook the onions until soft and golden, about 10 to 12 minutes.
3. Stir in the roast beef and garlic powder until warm. Season with salt and pepper.
4. Spread it in a greased 9×13 dish and cover with the cheese.
5. Bake 20 to 25 minutes while you heat the broth on the stove. Serve with the warm broth for dipping.

Common Mistakes to Avoid

• Rushing the onions. High heat burns them before they turn sweet. Keep the heat at medium and stir often.
• Cooking the beef too long. Deli roast beef only needs a minute or two in the pan. Any longer and it gets tough.
• Over-salting. Deli meat, cheese, and broth all bring salt. Taste before you season.
• Using pre-shredded cheese with a lot of starch. It can melt a little grainy. Shredding your own from a block melts smoother.

Variations

• Philly style: Add sliced green peppers and mushrooms with the onions.
• Richer au jus: Simmer the broth with a splash of Worcestershire sauce and a sprig of thyme.
• Horseradish kick: Spread a thin layer of creamy horseradish over the beef before adding the cheese.
• Not keto? Serve it over toasted hoagie rolls for a knife-and-fork French dip.

What to Serve With It

A crisp side cuts through the rich beef and cheese. Try a simple green salad, roasted asparagus, or garlicky green beans. Mashed cauliflower is a good low-carb stand-in for potatoes. Dill pickle spears on the side give you that deli feel. If you are not eating keto, oven fries or a baked potato are hard to beat.

Make Ahead, Storage, and Reheating

Make ahead: Caramelize the onions up to 2 days early and keep them in the fridge. You can also assemble the whole casserole a day ahead. Bake it straight from the fridge and add about 5 to 10 minutes.

Storage: Store the casserole and leftover broth in separate covered containers in the fridge for 3 to 4 days.

Reheating: Warm portions in the microwave for 1 to 2 minutes, or in a 350°F oven for 10 to 15 minutes. Heat the broth on the stove until steaming.

Keto French Dip Casserole FAQ

Is this casserole low carb?
Yes. The only real carbs come from the onion, which is spread across 4 servings. There is no bread, flour, or sugar.

What is au jus?
Au jus means “with juice.” It is a thin, savory beef broth served for dipping. Here, warm beef broth plays that role.

Can I use leftover roast?
Yes. Slice or shred it thin and use the same amount as the deli beef.

Can I make it in a smaller dish?
Yes. An 8×8 dish gives you a thicker layer. Bake a few minutes longer so the center is hot.

Tips for the Best French Dip Casserole

• Tear the beef into strips. Cutting or tearing deli slices into ribbons helps them mix evenly with the onions.
• Deglaze the pan. After the onions are golden, splash in 2 tablespoons of the beef broth and scrape up the browned bits. That flavor goes right into the casserole.
• Season the broth. Add a pinch of garlic powder and black pepper to the warm broth so the dip tastes like real au jus, not just broth from a carton.

Leftover Ideas

Leftovers make great low-carb lunches. Roll warm portions in large lettuce leaves for French dip lettuce wraps, with a small cup of broth on the side. Spoon it over a bowl of cauliflower rice, or fold it into a cheese omelet for a hearty breakfast. If you are not eating keto, pile it on a toasted hoagie roll for a classic sandwich.