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1
For the cake: Preheat the oven to 350 degrees F. Adjust the rack to the center of the oven.
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2
Spray two 9-inch round cake pans well with nonstick spray.
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3
Add the flour, granulated sugar, cocoa powder, baking powder, baking soda and salt to the bowl of a standing mixer fitted with the whisk attachment.
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4
Turn on the mixer and allow the dry ingredients to blend for a full minute.
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5
Turn the mixer up and, while the mixer is running, add the eggs, one at a time, the buttermilk, warm water, melted butter and vanilla extract.
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6
Beat until combined, about 2 minutes.
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7
The batter will be thick.
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8
Evenly divide the batter between the prepared pans.
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9
Tap the bottom of the cake pans on the counter to release any air bubbles.
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10
Bake until a toothpick inserted into the center of the cake comes out clean, about 30 minutes.
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11
Cool in the pans for 10 minutes, and then turn out onto a wire rack to cool completely before frosting.
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12
For the frosting: Add the butter to a medium saucepan over medium heat.
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13
Add the chopped chocolate and stir to melt.
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14
Remove from the heat.
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15
Stir in the cocoa powder and vanilla extract.
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16
Using an electric hand mixer, beat in the confectioners' sugar.
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17
Slowly beat in the sour cream.
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18
Let cool for 20 minutes.
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19
Frost the cake by first spreading the frosting between the layers.
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20
Then top with cake, and continue frosting the top and the sides.
