Here's a great way to get an extra meal from leftover roast beef. For a do-it-yourself sandwich buffet, set out a platter of thinly sliced roast beef with condiments such as pepper jelly and Dijon, some crumbled or thinly sliced cheese and baby arugula. Even broken pecans or walnuts are a nice touch as a topping. Make sandwiches with Kaiser buns for a he-man style sandwich.
Divide beef, cheese, onion and broken nuts among each of the 4 rolls; set aside.
Combine mayonnaise and mustard; spread mixture on the 4 bun tops.
Season with salt and pepper to taste.