For the Cake

1. Preheat the oven to 350°F. Line two 6-inch pans with parchment paper or grease and flour the edges.
2. In a large mixing bowl, combine the sugar, vegetable oil, eggs and vanilla extract. Beat on medium speed until the eggs and oil are well incorporated and the batter is lighter in color. Next, mix in the sour cream and beat until well combined.
3. In a separate bowl, sift together the dry ingredients. Alternate adding half of the dry ingredients and half of the coffee at a time. Mix until well combined, then use a spatula to scrape down the sides of the bowl and stir the batter to ensure it’s well mixed.
4. Divide the batter evenly between the two pans, about 1 1/4 cups batter per pan. Bake at 350°F for 20-24 minutes. Test the cake for doneness by inserting a toothpick into the center of the cake. If the toothpick comes out clean, the cake is done. Cool completely prior to frosting.

For the Frosting

1. Cut the butter into pieces, 1 tablespoon each. Using the paddle attachment, whip the butter for 3-5 minutes, scraping down the bowl occasionally. Beat until the butter is whipped, fluffy and easily spreadable. 
2. Sift the cocoa powder into a mixing bowl, then add the vanilla extract. Turn the mixer to slow speed and beat until the cocoa power and extract are mixed into the butter.
3. Add the powdered sugar and 1 tablespoon of heavy cream and mix on medium-low speed until fully incorporated. Then, increase the speed to medium-high and beat for another 2-3 minutes to whip additional air into the frosting. If the frosting still seems thick, add an additional 1/2-1 tablespoon heavy cream.

For the Assembly

1. Use a cake leveler or serrated knife to cut the domes off the top of the cake. Place a dollop of frosting on your cake board and place the bottom layer of cake on top of that.
2. Fill a large piping bag with the frosting and cut off the end of the piping bag about 1/2 inch up. Pipe a layer of frosting on top of the first layer, starting at the outside edge and working your way into the middle. Spread evenly with an offset spatula. Place the next layer on top.
3. Use the piping bag to fill in the sides of the cake with frosting. Use an offset spatula or icing smoother to wipe away the excess frosting. Decorate with the remaining frosting using a large closed star tip (Ateco 846) or garnish with sprinkles or fruit.