Cut the onion into small cubes and fry. Also cut the garlic clove into small pieces, add to the onions with the tomatoes and bring to the boil briefly. Cut the mozzarella into small cubes and add to the sauce along with the cheese. When the cheese has melted, add the cream, tomato paste, herbs and spices. Simmer for another 5 - 10 minutes while stirring on a low level.
If the sauce is too thin, either add 1 - 2 tablespoons of tomato soup powder to the sauce or add cornstarch or make a roux.