
This Halloween layer cake has three layers of rich chocolate cake, and is covered in orange-tinted Swiss buttercream, a ganache glaze, and Halloween sprinkles.
Preheat your oven to 350 degrees. Spray three 9-inch cake pans with baking release spray (nonstick cooking spray with added flour).
In the bowl of a stand mixer, stir together the flour, sugar, cocoa powder, baking soda, baking powder and salt.
In another mixing bowl, whisk together the eggs, buttermilk, coffee, vegetable oil and vanilla.
Add the wet ingredients to the dry. Stir on low speed until all of the dry ingredients are moistened, then beat on medium speed until the mixture is smooth, about 3 minutes. Scrape down the sides and bottom of the bowl about halfway through mixing.
Divide the batter between the three prepared pans. Bake for 35 minutes, or until a toothpick inserted in the center of the cake comes out clean.
Cool the cakes in the pans on a wire rack for 15 minutes, then remove from the pan and cool on the wire rack completely.
Bring about an inch of water to a simmer in a small saucepan.
In the bowl of a stand mixer, whisk together the egg whites and sugar.
Set the mixing bowl over the simmering water. Use a handheld mixer with beater attachments (or whisk by hand) to continuously beat the mixture while heating the whites and sugar, until the sugar dissolves (you should not feel any grittiness when rubbing the whites mixture between your fingers).
Once the sugar dissolves, place the mixing bowl on the stand mixer fitted with the whip attachment. Beat on medium-high speed until the whites are stiff and glossy, and the outside of the bowl reaches room temperature.
Lower the speed to medium-low, and begin adding the butter, 2 tablespoon at a time at first, mixing until fully incorporated before adding more. As you get closer to the end, reduce the additions to 1 tablespoon chunks.
Once all of the butter is added, return the speed to medium-high, and beat until the buttercream becomes smooth and silky (about 5 minutes of mixing). If it doesn't, chill the mixing bowl and whip attachment for 10 minutes, then continue whipping until the buttercream comes together.
Beat in the vanilla, then the white chocolate, and beat until fully and evenly incorporated.
Begin to add the food coloring, a little at a time, beating to fully incorporate before adding more, until it reaches the color you want (remember that the color will darken as the frosting sets.
Level each cake by using a serrated knife to cut off any domed parts from the top of each cake.
Place one cake, cut-side down, on a cake board. Frost with 1/2 cup of the buttercream.
Place another cake, cut-side up, on top of the first cake. Frost with another 1/2 cup of frosting.
Place the third cake cut-side down. Spread a very thin layer of frosting on top, and around the sides of the cake. Refrigerate until well-chilled, about 30 minutes.
Spread a thicker layer of frosting on the top and sides of the cake. Refrigerate about 15 minutes, then use the plain side of a cake comb to smooth the icing.
Refrigerate while you make the chocolate glaze.
Place the chocolate chips in a glass or metal bowl.
Heat the cream in a small saucepan over medium-high heat. Watch it carefully and bring it to scalding (small bubbles form at the edge of the pan). WIth this small amount of cream, it will happen quickly.
Pour the cream over the chocolate chips and let stand for 1 minute, then whisk until smooth.
Place an offset spatula near the cake. Pour the glaze over the center of the cake, and use the offset spatula to guide the glaze to the edges of the cake and allow it to spill over. Work quickly, because the chilled cake will quickly set the ganache.
Fit a piping bag with an open-star piping tip. Fill halfway with orange frosting. Pipe rosettes all around the edge of the top of the cake, and pipe shells around the bottom edge of the cake.
Shake the sprinkle mix over the top of the cake.
Chill until ready to serve.