• Preheat oven to 350 degrees F. Grease 3 8-inch round cake pans. Line with parchment circles (if you want) then grease and flour again.
• Whisk together flour, baking powder and salt; set aside.
• Cream the butter and sugar in bowl of a stand mixer using paddle attachment. Beat in the vanilla.
• Add eggs one at a time, beating well after each addition. Scrape side of bowl often.
• By hand or using lowest speed of mixer, beat in the flour and milk alternately, beginning and ending with the flour mixture.
• Divide batter in half. If you have a scale, set a second bowl on it, set tare to zero and weigh out about 17 oz which is about half the batter.
• Stir the melted chocolate into half the batter.
• Divide batter evenly between 2 decorating bags (or two freezer bags) filling about halfway full (you can add more batter to the bags later). Snip the ends off to make an opening of about half an inch.
• Starting with the vanilla batter, make a circle around edge of one cake pan. Pipe a circle of chocolate inside the vanilla circle. Make the middle circle with chocolate. Repeat in a second pan starting with a ring of chocolate around the edge. Repeat in third pan starting (again) with the vanilla.
• Bake pans on center and lower racks, staggered, for 20 to 25 minutes or until a toothpick inserted in cakes comes out clean. Let cool in pan set on a rack for 10 minutes. Remove from pans and peel off parchment. Cool completely.

Frosting

• Make frosting and stack cakes to form a checkerboard.
• Frosting: Beat together softened butter (it should not be cold at all, just warm but not melted) and some of the powdered sugar. Add chocolate(s) and continue mixing. Add vanilla and cocoa powder. With mixer on low, continue adding remaining sugar. Add milk. Increase speed to high and beat until frosting is smooth and creamy.