Preheat oven to 325. Grease and flour bundt pan, set aside. Cream butter in large mixing bowl. Add sugar, beat until light and fluffy. Add eggs, one at a time, beating well after each addition.
In separate bowl, stir together flour, cocoa, and baking powder. Measure milk and stir vanilla into it. Add milk and dry ingredients alternately to batter in mixing bowl, mixing after each addition. Pour into pan and bake for one hour and twenty minutes. Let cool for ten minutes before removing from pan and allowing to cool completely before adding glaze.
For glaze, Combine sugar, cocoa, milk, shortening, margarine, and salt in heavy saucepan. Bring to a rolling , stirring constantly. Once it reaches a rolling boil, allow to boil without stirring for two minutes. Remove from heat and add vanilla. Stirr until cooled just slightly. Spoon over cooled cake.