Preheat the oven to 400ºF.
In a small saucepan over medium heat, combine water and homemade au jus mix. Whisk until liquid begins to boil.
Lower temperature and simmer for 15 minutes or until gravy is slightly thickened. Optional: Add a dash of soy sauce to your au jus.
While the au jus is cooking, layer ¼ lb of beef and 2 slices of cheese inside each roll.
Optional: spread a little worcestershire sauce on your roll and add onion slices under the cheese slices.
Place rolls into a baking dish.
Brush melted butter onto the top of each roll. Optional: sprinkle each with a little salt.
Place in the oven on the center rack. Cook for 5-6 minutes or until the tops of the rolls are golden and slightly crispy.
When au jus is slightly thickened, remove from heat. Pour into 4 small dipping bowls.
Serve sandwiches with au jus.