Instructions

1. Preheat oven to 350 degrees, w/racks in upper and lower thirds. Cut 2-8 in. rounds of parchment paper to line the bottoms of 2-8 in. round cake pans. Butter and line pans. Butter linings. Dust pans with cocoa. Set aside.
2. Sift together cocoa, flour, sugar, baking soda, baking powder, and salt into the bowl of an electric mixer. Fit mixer with paddle attachment. Add eggs, yolk, water buttermilk, oil and vanilla. Mix on low speed until smooth, about 3 minutes.
3. Divide batter into pans. Bake, switching and rotating pans halfway through cooking time, until toothpick inserted in center comes out clean, about 40 minutes. Let cool in pans on wire rack for 30 minutes. Run thin knife around edges of pans to loosen. Unmold and peel off parchment. Let cool completely, top sides up, on racks.
4. Frost and assemble to your liking.

5. fattening!