Select a fish that weighs two or three pounds. Rub inside and out thoroughly with mixture of one-half teaspoon of black pepper, dash of cayenne pepper and one small clove of garlic minced.
Place one and one-half tablespoons of butter in large frying pan. Cut in very small pieces six shallots, using green as well as white and add them to the butter.
Then place fish in pan. Sauté for ten or fifteen minutes, then turn and cook same length of time on the other side.
Make a sauce of one tablespoon of butter, two tablespoons of flour and two cups of boiling water. Let cook a few minutes. Then add yolks of two well-beaten eggs and one can of mushrooms chopped fine. Add salt and pepper to taste and cook a few minutes until it begins to thicken. Then mix with sauce in frying pan.
Place flounder in a covered baking dish. Pour sauce over fish, cover, and bake in a hot oven to twenty to thirty minutes.
Serve hot, in baking dish and small triangles of hot, buttered toast with it.