Quick Roast Beef on a Bun

If you ask me, roast beef on a bun is one of those classic sandwiches that never gets old.

This hearty sandwich brings together tender slices of roast beef and soft, fresh buns in a way that just feels like home. The meat is perfectly cooked and piled high, making every bite satisfying and comforting.

It’s topped with your choice of traditional fixings – maybe some crispy onions, melted cheese, or a spread of creamy horseradish sauce. The combination is simple but completely hits the spot.

It’s a no-fuss meal that works for both casual weeknight dinners and weekend lunch gatherings, especially when you’re craving something substantial and satisfying.

What Kind of Roast Beef Should I Use?

For a great roast beef sandwich, you’ll want to start with the right cut of meat. Top round (also called London broil) is a popular choice because it’s lean and slices really well, but you could also use bottom round or sirloin tip if that’s what you find at your store. When buying your roast beef, look for meat with good marbling but not too much visible fat – this will give you the best flavor without making your sandwich greasy. If you’re short on time, good-quality deli roast beef works fine too, just ask them to slice it extra thin so it stays tender and easy to bite through.

Options for Substitutions

This sandwich recipe is pretty adaptable – here are some helpful swaps you can try:

• Butter: You can use salted butter instead of unsalted – just reduce the added salt by 1/4 teaspoon. Margarine works too, though the sauce won’t be quite as rich.
• Milk: Any milk fat percentage works fine here. For a richer sauce, try half-and-half. Non-dairy folks can use unsweetened almond or oat milk, but the sauce might be slightly thinner.
• Sharp cheddar: Feel free to mix up the cheese – try provolone, Swiss, or American cheese. You can even do a combo! Just make sure to use a good melting cheese.
• Dijon mustard: Yellow mustard or whole grain mustard work well too. If you’re not a mustard fan, you can leave it out, but you’ll miss some of that nice tang.
• Sesame seed buns: Any sturdy roll works here – try onion rolls, kaiser rolls, or plain burger buns. Just avoid super soft bread that might get soggy under the sauce.

Watch Out for These Mistakes While Cooking

The biggest challenge when making roast beef on a bun with cheese sauce is getting the roux right – rushing this step can leave you with a lumpy or floury-tasting sauce, so take your time to cook the butter and flour together until it’s golden and smells nutty. A common mistake is adding cold milk to your roux too quickly, which can create lumps – instead, warm your milk slightly and add it gradually while whisking constantly. When it comes to the cheese, shredding it yourself rather than using pre-shredded varieties will give you a smoother sauce, as pre-shredded cheese often contains anti-caking agents that can make your sauce grainy. For the best sandwich assembly, make sure to warm your roast beef slightly before adding it to the bun, as cold meat can cool down your cheese sauce too quickly and make it thick and gloppy.

What to Serve With Roast Beef Sandwiches?

These hearty roast beef sandwiches pair perfectly with classic deli-style sides that’ll make you feel like you’re at your favorite sandwich shop. A crunchy dill pickle spear on the side is pretty much a must-have, and a handful of kettle-cooked potato chips adds that satisfying salty crunch. For something fresh, try a simple coleslaw or a small side of macaroni salad – both add nice contrast to the rich, cheesy beef sandwich. If you’re feeding a crowd, putting out a bowl of crispy onion rings or some french fries lets everyone grab what they like.

Storage Instructions

Keep Fresh: If you’ve got leftover assembled sandwiches, wrap them individually in aluminum foil or plastic wrap and pop them in the fridge for up to 2 days. For best results though, I recommend storing the cheese sauce and roast beef separately from the buns – this keeps the bread from getting soggy.

Save Components: The cheese sauce will stay good in an airtight container in the fridge for up to 4 days. Your sliced roast beef will keep well for 3-4 days when stored in a sealed container. Keep the buns at room temperature in their bag or bread box for 2-3 days.

Warm Up: When you’re ready to eat, warm the cheese sauce in the microwave in 30-second intervals, stirring between each until smooth. Heat the roast beef briefly in a pan or microwave until just warm. Toast the buns if you like, then assemble your sandwich with the warmed components.

Preparation Time	10-15 minutes
Cooking Time	20-30 minutes
Total Time	30-45 minutes
Level of Difficulty	Medium

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 1200-1400
• Protein: 60-70 g
• Fat: 70-80 g
• Carbohydrates: 90-110 g

Ingredients

For the cheese sauce:

• 3 tbsp unsalted butter
• 1/2 tsp salt
• 1 1/2 tsp dijon mustard (I prefer Grey Poupon)
• 1 1/4 cups milk
• 6 oz sharp cheddar cheese (shredded from a block for best flavor)
• 2 1/2 tbsp plain flour

For the sandwiches:

• 1 batch easy roast beef, sliced thin
• 3 sesame-seed burger buns (toasted for extra flavor and texture)

Step 1: Prepare the Cheese Sauce Base

Begin by placing a pot over medium heat and melting the butter.

Once the butter has completely melted, add flour to the pot.

Whisk the mixture continuously until all lumps are eliminated, creating a smooth base for the sauce.

Step 2: Add Liquid Ingredients and Thicken

Slowly whisk in the milk, mustard, and salt into the butter-flour mixture.

Continue to whisk until the mixture becomes smooth and free of lumps.

Keep whisking the mixture until it has slightly thickened to create a rich and creamy texture.

Step 3: Incorporate the Cheese

Remove the pot from heat.

Gradually stir in grated cheese, adding it in small handfuls at a time.

Ensure that each addition is fully melted and integrated into the sauce before adding more.

Continue this process until all the cheese has been incorporated, resulting in a smooth cheese sauce.

Step 4: Assemble the Sandwiches

Take the bottom bun of each burger and stack a third of the roast beef onto it.

Generously pour the cheese sauce over the roast beef.

Place the top bun gently onto each sandwich, pressing down slightly to keep everything in place.

Serve immediately for the best experience.