Leftover homemade Roast Beef is a very convenient part of many deferent dishes and especially for hearty, satisfying sandwiches for meat lovers.
Here is one sandwich that has all components of a French Onion Soup, except of the beef slices. I think even if you make the same sandwich without beef, it will still be very tasty.
Heat oil and butter in a medium nonstick skillet over medium heat.
Add onion and cook stirring until lightly browned, about 15 minutes.
Deglaze with beef broth and cook until it is absorbed, about 10 more minutes.
Add the dry sherry, cook stirring, until no liquid is left in the skillet and onions have caramelized to a deep brown color, mix in parsley.
Preheat oven to 425 degrees.
Meanwhile, slice the bread and spread butter on one side. Place on baking sheet, buttered side up, and toast on the upper rack, until golden about 7-10 minutes. In a small sauce pan heat the leftover jus.
To assemble; top the buttered sides with 1 half slice of cheese, then about a tablespoon of the onion mixture. Dip beef slices into hot jus and arrange 4 slices on top of onion mixture, cover with the other half of cheese.
Return to the oven and bake until cheese has melted.
Serve with extra jus for dipping, if eating right away.
The jus can be substituted with any your favorite sauces (I love Chimichurri).