Ingredients

The following ingredients have 12 Servings
  • 2 cups granulated sugar
  • 1 3/4 cup all-purpose flour
  • 3/4 cup dark or Dutch-processed cocoa powder, sifted
  • 2 teaspoons baking soda
  • 1 teaspoon baking powder
  • 1 teaspoon fine sea salt
  • 1 1/2 teaspoons ground cinnamon
  • 1/4 teaspoon ground cloves
  • 1/4 teaspoon ground nutmeg
  • 1 cup sweet potato puree (canned or fresh)
  • 3 large eggs
  • 1/2 cup vegetable oil
  • 1 1/2 teaspoons vanilla extract
  • 1 cup full-fat buttermilk
  • 3.5 ounces dark or semisweet chocolate, finely chopped
  • 1/3 cup heavy cream
  • 1 tablespoon unsalted butter, cut into cubes
  • 10 large egg whites (about 10 ounces)
  • 3 cups granulated sugar
  • 1/4 cup plus 2 tablespoons molasses, divided
  • 2 pounds (8 sticks or 4 cups) unsalted butter, room temperature
  • 1 teaspoon vanilla extract

Instruction

  • Preheat oven to 350ºF, position oven racks at 1/3 and 2/3 positions. Butter and line the bottoms of three 8-inch round cake pans with parchment paper; butter parchment.To prepare cake layers, whisk together sugar, flour, cocoa, baking soda, baking powder, salt, and spices in a large bowl or the bowl of a stand mixer.In a separate bowl, whisk sweet potato puree with eggs until smooth. Whisk in oil and vanilla extract.Make a well in the bowl with the dry ingredients and add sweet potato mixture and buttermilk. Mix on low speed until dry ingredients are just incorporated, scraping down the sides of the bowl as necessary.Divide batter among prepared baking pans; you’ll use approximately 2 cups of batter per pan. Bake for 30 to 40 minutes, rotating pans halfway through baking, until a toothpick inserted near the center comes out clean.  Place pans on wire baking racks and let cool to room temperature.Run a knife around the edge of each cake pan then invert onto a wire rack. The cake should come out cleanly. Remove parchment and let cool completely before assembling, or ideally, wrapping each layer with two layers of plastic wrap and sealing in a zip-top bag and freeze (frozen layers will be easier to level and assemble later).To prepare ganache, place chopped chocolate (the finer the better) in a heat-proof bowl.  Warm cream over medium-low heat until it just starts to steam (do not let it boil). Pour over chopped chocolate and let sit for 30 seconds. Slowly and gently whisk, starting with small concentric circles in the center of the bowl, until chocolate is melted and ganache is smooth. Add butter, a little bit at a time, gently whisking until incorporated. Refrigerate for 30 to 40 minutes or until thickened and spreadable.Meanwhile, to prepare buttercream, combine egg whites, sugar, and 2 tablespoons molasses in a heat-proof bowl set over (but not touching) a pot of boiling water. Or if you have a large double boiler pot you can use that instead. The idea is to gently heat the egg so it is warm but not scrambled, as it would if you heated it directly. Whisk until sugar is completely dissolved and mixture is warm to the touch (it should measure 140ºF on an instant-read thermometer). Transfer to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium high speed until the meringue is completely cool; bowl should not have even a hint of heat at the base when you touch it. This can take quite a while, upwards of 45 minutes even, so just keep mixing until it’s completely cool.Once cool, switch to the paddle attachment and begin to add butter, 1 tablespoon at a time, mixing well after each addition. Do this slowly, as adding the butter too quickly could cause your buttercream to separate. Once all the butter has been added increase speed to high and beat until thickened and fluffy (you’ll see a visible change in the consistency as you add the last bits of butter). Add vanilla and additional 2-4 tablespoons of molasses (to taste) and mix thoroughly. Use immediately, or cover and refrigerate until ready to use. If refrigerated, let the buttercream warm to room temperature before using and beat it again until the fluffy texture returns.To assemble cake, level each cake layer by cutting of the domed top with a long serrated knife. Place one cake layer on a cake stand or serving plate. Top with 1/2 cup of buttercream and spread to edges with an offset spatula. Top with half of ganache, spreading into a smooth layer. Place second layer on top, gently pressing to adhere. Repeat with another 1/2 cup of buttercream and remaining ganache, then top with third and final layer, flat side up.Cover the entire cake with a thin layer of buttercream. This “crumb coat” will keep the stray crumbs in place and make frosting the cake easier. Refrigerate for about 15 minutes to allow this crumb coat to set, then spread the thicker final layer of buttercream on top of that, smoothing out top and sides as best you can. There will be a good amount of buttercream left, which you can use to pipe decorative details onto your cake if desired. Optionally top cake with meringue cookies and a dusting of cocoa powder before serving at room temperature.