Preheat the oven to 350 degrees F. Butter and line the bottom of 2 (8-inch) cake pans
In a large bowl, mix together the flour, sugars, cocoa, baking powder, baking soda and salt. In another bowl or wide-necked measuring cup whisk
together the eggs, sour cream
and vanilla until blended. Using a standing or handheld electric mixer, beat together the melted butter and corn oil
until just blended (you'll need another large bowl for this is using the hand mixer
; the standing mixer comes with its own bowl), then beat in the water. Add the dry ingredients all at once and mix together on a slow speed. Add the egg mixture, and mix again until everything is blended and then pour into the prepared tins. And actually, you could easily do this manually; I just like my toys and find the stand mixer a comforting presence in itself.
Bake the cakes
for 45 to 50 minutes, or until a cake-tester comes out clean. Cool the cakes in their pans on a wire rack for 15 minutes, and then turn the cakes out on the rack to cool completely.