This decadent chocolate cake is the only recipe you need. It's moist and fudgy with a delicious chocolate flavor and can be adapted to a variety of pan sizes. Make it as a layer cake and decorate with chocolate frosting for the ultimate chocolate dessert.
Line the bottom of two 8-inch round cake pans with parchment paper. Grease the sides of the pans, and lightly dust with cocoa powder. Set aside. *The sides of your pans must be at least 2.5 inches tall (5 cm). See recipe notes for additional pan sizes.
In a very large bowl whisk together the flour, cocoa, baking soda, baking powder and salt. If the cocoa is lumpy, sift the cocoa first.
In a separate large bowl whisk together the oil, sugar, eggs and vanilla extract. You can do this by hand or with an electric mixer. Then carefully whisk in the buttermilk.
Carefully whisk the wet ingredients into the dry ingredients until there are no lumps. Very carefully whisk in the hot coffee.
Pour the batter evenly between the two prepared cake pans and bake for 35-40 minutes until an inserted toothpick comes out clean. Allow the cakes to cool in their pans for at least 30 minutes before removing and continuing to cool on a wire rack.
In a very large bowl, beat the butter until smooth and fluffy.
Starting with the mixer on low speed, beat in 2 cups powdered sugar. Sift the powdered sugar first if it's lumpy.
Beat in the cocoa powder and salt, again starting with the mixer on low speed. Sift the cocoa if it's lumpy.
Beat in the rest of the powdered sugar about ½ - 1 cup at a time, alternating with 1-2 tablespoons of cream until the desired sweetness is reached and the frosting is thick and creamy.
Assembling the Cake
Ensure the cakes are completely cooled before getting started.
If your cake layers are domed on the top, use a serrated knife to gently saw off the rounded top.
Place one cake layer top side down on the plate or cake stand that you plan to serve it on. Frost the top of the layer to create an even layer about ¼ - ⅓ inch thick.
Place the second cake layer on top, top side down.
Frost the sides and top of the cake with a swirly layer of frosting. If cake crumbs are getting mixed into the frosting, frost the sides with a very thin layer of frosting (this is a crumb coat). Place the cake in the fridge for 1 hour (keep the frosting at room temperature). Then remove the cake from the fridge and frost the sides and top with a thick layer of frosting.
Pan Sizes & Baking Times:
Two 8-inch (20 cm) round cake pans with high sides (2.5 inches/5 cm) - 35-40 minutes
Two 9-inch (23 cm) round cake pans - 30-35 minutes.
Three 8-inch (30 cm) round cake pans - 30-35 minutes.
A 9x13 inch (23x33 cm) cake pan - 35-40 minutes. If using a 9x13 inch pan, grease the bottom and sides of the pan and lightly dust with cocoa powder. I do not recommend inverting the cake pan. Simply frost the top and serve from the pan. Divide the frosting recipe in half.
I used Dutch-processed cocoa for a more intense chocolate flavor. Natural cocoa powder works too.
To make your own buttermilk, add 1 tablespoon of white vinegar to a liquid measuring cup. Fill to the 1 cup line with milk. Give it a stir, then let sit for 5 minutes before using.
Hot coffee can be substituted for boiling water.
Storage & Make Ahead Tips
Unfrosted cake layers can be stored in an airtight container at room temperature for up to 2 days, or in the fridge for up to 5 days.
Unfrosted cake layers can be wrapped tightly in plastic wrap, then wrapped in tinfoil or placed in a freezer container and frozen for up to 2 months. Thaw in the fridge. Do not thaw at room temperature or the cake will become gummy. Freeze each layer individually.
Store frosted cake covered at room temperature for up to 8 hours, or in the fridge for up to 5 days. Let the cake sit at room temperature for 30 minutes before enjoying for the frosting to soften.
Nutrition information is an estimate only and based on 1 slice, assuming all the frosting is used and the cake is sliced into 12 equal pieces.