Prime Rib Sandwich

Prime rib sandwich days are my favorite because they usually mean I had a feast the night before. Whether it was a holiday dinner party, a celebration, or just a Sunday roast with the family, leftover prime rib is a culinary gift that keeps on giving. And while reheating slices is perfectly acceptable, turning that rich, juicy beef into the best prime rib sandwich you’ll ever eat is the move.

This prime rib sandwich comes stacked with buttery sauteed onions and mushrooms, melty provolone, and a punchy horseradish mayo that gives each bite a little kick. When stuffed inside a sturdy roll or baguette, it hits the mark right between decadent and casual. You’ll be thinking about this sandwich before you even finish the initial prime rib meal. Serve it with your favorite summer side dish, whether that’s potato salad or crunchy coleslaw.

Ingredients for Prime Rib Sandwich

• Butter: Butter creates a rich base for the onions and mushrooms to soften and caramelize. Use a good-quality butter for the best flavor payoff.
• Onion: Thinly sliced onion cooks down into a sweet, jammy layer that balances the beef’s richness. Yellow onions are a solid choice, but sweet onions will give a softer flavor.
• Fresh mushrooms: Any type of mushroom will add earthy, umami depth that makes these prime rib sandwiches feel restaurant-level fancy. Cremini mushrooms are a great choice. Slice them evenly so they cook at the same rate and don’t get soggy.
• Garlic: One clove is all you need to bring a warm, aromatic boost to the whole skillet situation.
• Au jus gravy mix and water: That little packet of mix at the grocery store is your best friend in this recipe. It creates a quick, flavorful, savory sauce that ties everything together and keeps the sandwich juicy. If you saved the drippings from the prime rib and you like a little extra fuss, you can make jus from scratch.
• Sauce: Mayonnaise, prepared horseradish and black pepper create a simple, creamy spread for the sandwich. If you made an elevated sauce with your prime rib dinner, use it instead.
• Leftover cooked prime rib: Thinly sliced prime rib is the star of the show—tender, juicy and already packed with flavor. Slice it as thin as possible so it layers beautifully on the sandwich. No prime rib? Thinly sliced roast beef from the deli will do.
• Arugula: Arugula adds a fresh, peppery bite that keeps the sandwich from feeling too heavy. It also brings crunch and brightness.
• French bread or baguette: A sturdy loaf is essential to hold all those glorious layers without falling apart. Look for bread with a crisp crust and soft interior. Looking to level up? Bake your own baguette.
• Provolone cheese: Provolone melts beautifully and adds a mild, creamy flavor that complements the beef. It gives you that irresistible gooey pull when you take a bite.

Directions

Step 1: Cook the onions and mushrooms

In a large skillet, cook the onions and mushrooms in butter until they’re tender. Add the garlic and cook for one minute longer, then add the gravy mix and water, stirring to combine. Cook until the liquid has reduced slightly, then remove the pan from the heat.

Step 2: Make the horseradish spread

In a large bowl, combine the mayonnaise, horseradish and pepper. Spread the mixture over the bottom half of the French bread.

Step 3: Build the sandwich

Top the bread with sliced prime rib, the mushroom-onion mixture and provolone cheese.

Editor’s Tip: Layering matters here. Start with the beef so the bread can soak up all that savory goodness, then pile on the veggies. Finish with the cheese, so it melts right over everything.

Step 4: Broil until melty

Preheat the broiler. Place the sandwich on a baking sheet and broil it 3 to 4 inches from the heat until the cheese melts, two to four minutes.

Step 5: Finish and serve

Top the sandwich with fresh arugula and the other half of the bread. Cut the sandwich into serving-size pieces.

Prime Rib Sandwich Variations

• Do it French dip–style: Serve these prime rib sandwiches with a side of warm jus, inspired by this French dip recipe.
• Swap the cheese: Use other good melting cheeses like Swiss, Gruyere or even sharp cheddar if you want a different flavor profile. Each one brings its own personality to the sandwich.
• Skip the mushrooms: Go all-in on deeply caramelized onions for a sweeter, less earthy profile.
• Spice it up: Add a swipe of Dijon mustard for a little extra kick. It cuts through the richness in a really satisfying way.

How to Store Prime Rib Sandwiches

If you have leftover prime rib sandwiches, wrap them tightly and refrigerate them. It’s best to store the components separately whenever possible. Keep the meat and mushroom mixture in an airtight container in the refrigerator and store the bread separately to avoid sogginess. Assemble the sandwiches fresh when you’re ready to eat again for the best texture.

How long will prime rib sandwiches last?

Prime rib sandwiches will last about three to four days in the refrigerator when they’re stored properly. After that, the quality of the meat and texture of the bread will start to decline.

Prime Rib Sandwich Tips

What’s the best way to make prime rib?

The best way to make prime rib is to cook it low and slow, then finish it with a high-heat sear for a crusty exterior and juicy interior. If you’re planning for sandwiches, slightly undercooking the roast helps keep leftovers tender when reheated. Make an herbed-crusted prime rib for extra flavor.

What’s the best bread for a prime rib sandwich?

The best bread for a prime rib sandwich is something sturdy like a French loaf or baguette that can hold up to juicy fillings. You want that contrast of a crisp crust and soft interior without the whole thing collapsing halfway through.

What can you serve with prime rib sandwiches?

Prime rib sandwiches go well with crispy fries or a simple green salad, but you can easily dig into any leftover side dishes—like mashed potatoes or creamed spinach—and serve them too.