Preheat oven to 325°.
Beat butter and shortening in mixer for 3 minutes.
Add sugar, beating for 7 minutes.
Add eggs one at a time, beating well.
Combine flour, cocoa, baking powder, and salt.
Add alternately with milk, beginning and ending with flour.
Stir in vanilla.
Pour batter into a greased and floured Bundt pan.
Bake at 325° for 1 hour and 30 minutes or until knife inserted into cake comes out clean. Cool in pan for 15 minutes. Remove from pan and cool on wire rack.