Combine butter, carob powder, and milk in saucepan and bring to a boil. Add vanilla and powdered sugar, and beat with electric mixer or by hand until smooth. Stir in nuts. Spread over hot cake. This cake always seems to be moister and to have a better flavor the day after it is baked. Note: This is a delicious cake to satisfy that chocolate craving for those who cannot eat chocolate. Carob powder may be purchased in many supermarkets and in health food stores.