Whipping up a quick sandwich means we're reaching for the deli meat here, but leftover roast beef from the night before is just as good and just as easy. You can throw together this roast beef sandwich in under 15 minutes without lacking in flavor!
Season potato slices with salt and pepper to taste. Add 1 teaspoon olive oil to a skillet and heat over medium heat. Add sliced potatoes and cook on both sides until lightly browned.
Remove potatoes from the skillet and set aside. Add onion to skillet and drizzle with balsamic glaze. Cook onions until soft. Remove onions and set aside.
Spread mustard on one side of the sandwich bun and horseradish mayo on the other side. Repeat for second sandwich.
Add roast beef, potatoes, onion, and cheese. Top with bun.
Notes
Allow your beef to come to room temperature before assembling. The same goes for the cheese.
We are using sliced deli roast beef, but this recipe is an excellent way to use leftover roast beef!
If you'd like a little crunch, replace the fresh white onion slices with crispy fried onions, which you can find at the grocery store.
Enjoy as-is or optionally toast in a toaster oven or skillet with a small amount of butter to crisp up the bread and melt the cheese.