Oil two 10-inch round and at least 4-inch high springform pans* with oil. If you only have one pan, make half the recipe at a time. Line the bottom with parchment paper and oil the top of the paper. Dust the sides of the pan with a mixture of flour and cocoa powder, about a teaspoon or two of each. Tap the pan on the sides and bottom to distribute the dry mixture evenly; set aside. Preheat the oven to 350°F.
In the bowl of your electric mixer, fitted with the paddle attachment, cream together the sugar, oil, sour cream, and oil on medium-low speed for 5 minutes or until the sugar breaks down.
Add the eggs one at a time, beating on medium-low until thoroughly combined before adding the next.
Add a third of the flour mixture at a time, alternating with half of the buttermilk, starting and ending with flour, beating on medium-low speed after each addition, just until combined. Then, add the vanilla and beat on low to combine.
Distribute the batter between the two pans. Bake 30 - 40 minutes (20 22 minutes for three layers) or until the cake bounces back when lightly touched. The first thing to test for is if the batter does not jiggle. Once it stops jiggling when lightly shaken, then lightly touch it. If it appears to be pretty firm but doesn’t spring back, it may need 2 more minutes, but 5 minutes may be too much. It is done when it springs back.
Remove from the oven and cool on a wire rack for 10 minutes or until the cake pulls away from the sides. Remove the ring and allow to cool for about 15 minutes. Invert on a wire rack or plate that has been oiled. Remove the parchment paper and place back on original wire rack to cool completely, about 90 minutes.
Piping the ganache on top of the cake in a spiral pattern creates a thick layer of ganache, which you can then spread out using an off-set spatula while applying light pressure. For a smooth finish, wipe the spatula clean on occasion using a damp cloth or paper towels. Then, dip your spatula in water before spreading out the ganache more.
*For Cupcakes: Half of the recipe makes 24 mini cupcakes and five standard cupcakes. Bake large cupcakes about 19 minutes and mini cupcakes 13 minutes or until this bring back one lightly touched.
To make this cake three layers, divide equally between three pans and bake for 20 - 22 minutes or until it springs back when lightly touched.