This is a fabulous recipe for an open faced French Onion Beef Au Jus sandwich. This is truly a knife-and-fork sandwich. I have made this countless times, and have no idea where I got the original recipe, or why I have never posted it here. It can be made in the oven, or crockpot. I have made it both ways, depending on how much time I have, and really notice no difference. One little tip I can share, is when you are toasting your bread in the oven, slice a small sliver off the bottom (round side) of the bread to make a flatter surface, that way when you pile on the beef, onion, and cheese the sandwich won't tip over when you put it back in the oven to melt the cheese. (it keeps it from being top-heavy).