3 ounces (85 grams) baking (unsweetened) chocolate
4 cups (508 grams) sifted cake flour
2 cups (400 grams) sugar
1 teaspoon (5 grams) salt
1-1/3 cups (316 milliliters) milk, room temperature
1 cup (225 grams) unsalted butter, softened
1 tablespoon (15 milliliters) vanilla
2 tablespoons (15 grams) baking powder
Melt chocolate in double boiler over hot water. Set aside to cool.
Grease and flour 3- 8-inch cake pans. Line with 8-inch parchment or wax paper circles. Grease circles.
Preheat oven to 350 degrees F.
Combine flour, sugar, baking powder and salt. Mix on low for about one minute until blended.
Add butter and 1 cup milk. Beat at medium speed for 1-1/2 minutes scraping sides of bowl often.
In another bowl, combine vanilla, remaining 1/3 milk and eggs. Beat lightly. Add to batter in three parts, beating at medium-high speed for 25 seconds after each addition. Scrape sides of bowl after each part.
Divide batter in half. Stir melted chocolate into half of the batter and mix well.
Place checkerboard cake divider in pan and hold down. Pour darker batter in center and outer rings. Pour lighter batter in middle ring. ONLY FILL PANS HALFWAY UP.
Remove divider carefully by lifting straight up. Rinse divider and dry.
Place divider in next pan and repeat dark-outside, light-middle and dark-center circle.
Remove and clean divider as before. Place in third cake pan. This time light layer-outside, dark layer-middle and light layer-inside circle.
Carefully remove and clean divider as before.
Bake for 15 minutes. Turn baking pans around and bake for 10 minutes more. Test for doneness with cake tester. Cool in pans on wire racks for 10 minutes. Remove from pans and cool completely on wire racks.
After cake is cool, stack so outside colors alternate. Use a THIN layer of frosting between layers.