Grease a 12" skillet with 2 tb butter or margarine; sprinkle with shallots or green onions; add mushrooms. Fold filets in half or thirds; place in pan. Add wine and water to just cover filets. Add lemon juice, parsley, salt and pepper. Cover with a circle of wax paper with a small hole cut in the center. Bring to a boil. Reduce heat; simmer 3 minutes. Remove filets to a serving plate; keep warm.

Blend flour and 1 tb butter or margarine (beurre manie.) Reduce liquid in skillet by half. Add beurre manie, a small amount at a time, stirring until sauce is smooth. Add cream; bring to a boil; correct seasoning. Remove from heat. Add remaining butter or margarine a little at a time, rotating skillet to effect a gradual melting. Pour over filets. Glaze quickly under the broiler or in a 425°F oven. (The purpose of the glazing is to improve the appearance of the dish, and could be omitted without changing the taste in any way.)