- Melt chocolate over hot - not simmering - water. Set aside to cool slightly.
- In a small bowl, combine flour, baking powder, and salt. Set aside.
- In a large bowl, cream the butter and sugar. Add eggs one at a time, beating after each addition. Add vanilla.
- Add milk and flour to butter mixture, alternating each until batter is smooth. Beat at medium-high speed for 30 seconds.
- Divide batter in half (approximately 3 cups). Stir melted chocolate into one half of the batter until uniform in color.
- Grease and flour bottoms and sides of cake pans. Place checkerboarddivider into one prepared pan. then pour in the two batters (light and dark) as described in the image.
- Place pans in the center of a preheated 350°F oven and bake for 25 minutes. Halfway through baking, turn pans around. Test for donenessby inserting a cake tester into centers - it should come out clean; cakes will also retract slightly from the sides when done. Allow the cakes to cool in the pans, sitting on racks for 10 minutes. Loosen sides with a spatula or knife and invert onto greased wire racks to cool completely.
- When cool, stack cakes so outside colors alternate. Use a very thin layer of frosting between layers so you don't upset the checkerboard effect.