Method

1. Combine the milk and cornstarch in a saucepan, and cook over medium heat until thickened, stirring constantly. Set aside and let cool at room temperature.
2. repare the cake mix as per directions for a 9 x 13 inch pan. Bake.
3. Cream sugar, shortening, and butter in a mixing bowl until light and fluffy. Add 1 tsp vanilla, and milk mixture. Spread over warm cake; let cool completely!
4. Combine melted butter and cocoa in a bowl; mix well. Add confectioners sugar, egg, hot water and vanilla. Mix well. Pour over cooled frosted cake.
5. Chill in refrigerator until set.