As soon as the mushrooms are ready and become edible to taste, reduce the heat to a minimum, add salt, pepper, nutmeg and cream, mix.. NOTE – if the cream is 10%, then add 2 tablespoons of flour, this will help them thicken. If you have 20-30% in the cream, then you will not need flour. By the way, if the sauce is too thick, you can add a little water to the desired consistency.