Made this for lunch today, only takes about 10 minutes to make. Take 2 slices of bread and put them in the oven middle rack at 350 degrees. While the bread is baking take a package of Roast Beef and 1 can of French Onion soup and place it all into a sauce pan and bring to a simmer. Shouldn't take longer than 5 minutes. Once at a simmer or 5 minutes has passed (don't let your bread burn) take out the bread and place roast beef on one side of the bread, and place 2 pieces of Swiss cheese on top. (Optional) Place raw onions down first before the Beef and Swiss cheese, for extra crunch and more oniony flavor. Place back into the oven for an additional 5 minutes or until the cheese is melted. Should look like this: Then use the leftover French Onion soup as an Au Jus for dipping your sandwich.