1. To make Beurre Manie, rub 2 tablespoons butter and 2 tablespoons flour together in your hands to form small balls.
2. Mince the mushrooms very fine.
3. Combine all the ingredients, except the Beurre Manie, and boil until almost dry.
4. Remove from heat and stir in the Beurre Manie to thicken the mixture.

Warning:
Do not allow the mixture to boil after you have added the Beurre Manie to it.