Chop the mushrooms into small pieces and toss in the hot butter for a few minutes. Add ½ pt. of milk and cook gently for about 10 min. Blend the flour with the other ½ gill milk, add to the mushroom mixture. Season well and boil until smooth and thick. Stir as the mixture cools. If wished add 1 tablesp. thick cream. Dust with cayenne pepper when the cases are filled.