For the sauce, peel the onions and cut into small cubes, chop or press the garlic. Clean the mushrooms and cut into thin slices.
Lightly fry the onions with the garlic in a pan with a little oil, add the mushroom slices and fry with them. Then add the chopped tomatoes and the tomato paste. Pour the cream on and simmer gently at a low temperature. If necessary, add milk if the sauce is too thick. Add the basil, not too sparingly, as this is what gives the sauce that special touch. Season with pepper and a little broth to taste.