Shear the fillet into two parts in width, so you get a rectangle that you add some salt and black pepper to. Optionally, you can prepare 2 smaller rolls.
Chop the carrots, mushrooms, garlic and celery. Stew vegetables in 2 tablespoons of oil. When soft, add diced mozzarella and minced meat. remove these from the heat and seasoning ingredients. Mix until you get a uniform mixture.
Spread the mixture on the beef tenderloin. Rolled and fix with pegs, sticks, or strong thread. Fry the roll in the rest of the oil until browned.
Put the roll in a deep dish, cover with finely chopped onions, grated tomatoes and bay leaf. Pour white wine in and stew for about 60 minutes.