1. In large saucepan, sauté onions in butter until softened, add sugar to caramelize. When golden brown, remove from pan and set aside.
2. In same pan, heat beef slices until warm. Add beef broth to moisten.
3. Split rolls and toast under broiler until light brown.
4. On both sides of roll spread thin layer of mustard.
5. Place cheese slice on bottom roll, layer the beef, top with onions and red pepper slices. Top with roll.
6. Serve it up Sassy with individual Au Jus sauce per sandwich.

Au Jus Instructions :

1.  In small skillet or saucepan, caramelize the onions in olive oil.
2. Add garlic and cook for two minutes.
3. Deglaze the pan with vinegar, then add Worcestershire sauce, stir constantly.
4. Add beef broth and bring to a light boil.
5. Reduce heat and simmer for 30 minutes. Strain broth and then return to pan.
6. In small custard cup with 2 tablespoons cold water, add teaspoon flour, stir to dissolve. Simmer additional 5 minutes until slightly thickened.