French dip sandwiches are so good and this casserole is no different. It's like a casserole and a sandwich all in one. You'll need to use a knife and fork on this one though, and maybe even a spoon to get all of the yummy goodness!
2 T. olive oil
2 large Spanish onions, halved and thinly sliced
4 c. beef stock/broth
1 package onion soup mix
2½ lb. sliced roast beef, cut into 1 inch strips
2 T. unsalted butter, divided and melted
12 slider size potato rolls
1 lb. sliced Swiss cheese
kosher salt
In a large pan over medium-low heat, heat olive oil for about 1 minute; add onions; cook, stirring infrequently, until brown and caramelized, about 35 minutes. Remove pan from heat; set aside.
In the same pan over high heat, combine beef stock/broth and onion soup mix; bring to a boil; reduce heat to a simmer; add roast beef slices; simmer beef for about 10 minutes. Remove the roast beef to a bowl; reserving stock/broth.
Preheat oven to 350 degrees. Grease a 9 x 13 inch casserole dish with 1T. melted butter.
Slice off the top halves of rolls; set aside. Place bottom halves of rolls in the casserole dish; top with caramelized onion and beef slices. Fill pan with just enough beef stock/broth to cover the beef; top with cheese slices; place on the top halves of the rolls; brush rolls with the remaining 1 T. butter; cover with aluminum foil.
Bake 25 minutes. Remove foil; bake on an upper rack until tops of rolls are golden brown, another 5 minutes.
Cut into individual sandwiches. Serve hot.
12 servings.