1) Preheat the oven to 350°F. Grease and flour three 8" or two 9" round cake pans.
2) Beat together the butter, oil, sugar, cocoa, and vanilla extract until they form a smooth paste. The sugar will stay granular.
3) Add the eggs one at a time, beating well and scraping the bottom of the bowl after each addition.
4) Add the flour alternately with the water, mixing at medium-low speed and beginning and ending with the flour. Once the last of the flour is added, mix briefly, just until smooth.
5) Divide the batter between the pans. Cakes will self-level in the oven, so there's no need to smooth the top with a spatula. However, it does help to remove any large bubbles by tapping the cake pans firmly on the counter 7 or 8 times.
6) Bake the cakes for 30 to 35 minutes, until their tops spring back and a cake tester inserted into the center of one comes out clean.
7) Cool in the pan for 5 minutes, run a spatula around the edges to loosen, and turn out onto a rack to cool completely. Frost and fill as desired; our Super-Simple Chocolate Frosting is a great choice.
Yield: 2 round 9" layers or 3 round 8" layers.