Preheat oven to 350ºF. Grease and lightly flour two 9-inch round cake pans or place a round of parchment in the bottom of each cake pan and butter the sides. In a medium bowl, combine flour, cocoa, baking powder, baking soda, and salt, and set aside. In a large bowl, cream butter and sugar on medium-high speed until light and fluffy, about 4 minutes.
Reduce speed to low, and add vanilla and eggs one at a time, scraping bowl after each addition. Alternately add flour mixture and milk (starting and ending with the flour mixture), while mixing on low speed. Continue to mix until smooth.
Pour into prepared pans. Bake for 30 to 35 minutes or until a cake tester inserted in the center of cake comes out clean. Cool completely on wire racks before frosting.