Preheat oven to 325 degrees F (165 degrees C). Grease and flour a 10 inch Bundt pan. Sift flour, baking powder, salt and cocoa. Set aside.
In a large bowl, cream butter, shortening, sugar, and vanilla until light and fluffy. Add eggs one at a time, beating well after each. Add flour mixture alternately with the milk. Mix well.
Pour into 10 inch Bundt pan. Bake at 325 F (165 degrees C) for 70 minutes or until a toothpick inserted into cake comes out clean. Let cool for 10 minutes in the pan, then turn out onto a wire rack and cool completely.