Dissolve 2-3 tablespoons of mustard in the wine, add salt and pepper to taste, and soak the steaks for at least 2 hours. Heat 1 tablespoon of butter in a pan and fry the chopped bacon. Add the chopped onions and some finely chopped mushrooms.
Sauté until they're left only in oil. Add salt and pepper while still hot, and then immediately add the sliced processed cheese and grated cheese. Stir until the cheese melts a little.
Make pockets in the steaks and fill them with the stuffing. Stick their edges closed with toothpicks or sew them with thread. Put them in a greased oven dish, add the wine and a bowl of hot water, cover the oven dish with foil and put it to bake for an hour.
Then, remove the foil and bake until finished.