To make hot roast beef sandwiches, preheat oven to 350 degrees Fahrenheit, instructs Food Network. Combine 1/4 cup of spicy mustard, 3 tablespoons of poppy seeds, 3 tablespoons of grated onion, 1 tablespoon of horseradish mayonnaise and a dash of Worcestershire.
Spread the dressing on the tops and bottoms of 12 slices hamburger buns.
One the bottoms, lay on slices of provolone and American cheeses. Top cheese
with thinly sliced roast beef, and cover with the top buns. Wrap each in
foil, and bake for 15 to 20 minutes.
For a make-ahead sandwich, combine 1/4 of cup sour cream, Betty Crocker tells us, 1/4 cup of mayonnaise and 2 tablespoons of Dijon mustard. Cut one loaf of French bread in half horizontally. Spread the dressing on the inside of both halves. On the bottom, layer 1 pound of thinly sliced cooked roast beef, one 7-or 7.25-ounce jar drained and sliced roasted red bell peppers, and three leaves of romaine lettuce torn in half lengthwise. Cover with the bread top.
Wrap the sandwich all in plastic. Refrigerate for one to two hours. Cut into eight pieces before serving.