Make the Cake: Preheat oven to 350 degrees F. Grease and flour two 8-inch round cake pans; set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt; set aside.
Using an electric mixer, cream together butter and sugar until light and fluffy, about 3 to 5 minutes. Scrape down the sides of the bowl and beat in the eggs, one at a time, beating for 1 minute between each addition. Beat in vanilla extract.
Add the dry ingredients all at once and beat on low speed until just combined. Add the buttermilk and beat on low for 1 minute, then increase the speed to medium and beat for 3 additional minutes.
Divide the batter evenly between the prepared pans. Bake for 33 to 38 minutes, or until a skewer inserted into the center of the cake comes out with just a few moist crumbs attached. Remove from the oven and cool for 10 minutes in the pans, then turn out onto wire racks and cool completely before frosting.
For The Frosting: Met the butter in a small sauce pan over low heat. Add the cocoa, stir until the mixture is smooth and thick. Remove the pan from the heat and place the coca mixture into a medium size bowl. Let it cool slightly.
Add the milk and vanilla alternately with the powdered sugar to the bowl until you have the spreading consistency you desire.