When meat has cooked, remove to serving plate and increase temperature in skillet. Add mushrooms and saute until cooked. Add enough flour to pan to make a paste. Cook and stir about 3 minutes. Add milk as needed to reach desired consistency.
If you use a wire whisk you are less likely to get lumpy gravy and will be able to add milk more easily if it becomes too thick.
From: Glorious Grub Cookbook By. Joan Stewart