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1
Preheat oven to 350 F. Grease five 8-inch round cake pans and line the bottoms with parchment paper. Set aside.
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2
In a large bowl, whisk the flour, baking powder, baking soda and salt. Set aside.
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3
In another bowl, whisk the boiling water and cocoa powder until smooth. Set aside.
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4
Beat together the butter and sugar on medium speed in the bowl of a standing mixer until light and fluffy. Beat in eggs, one at a time. Beat in buttermilk and vanilla extract.
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5
Reduce the speed to low and beat in 1/3 of the flour mixture, followed by half of the cocoa mixture. Repeat with another 1/3 of the flour mixture and the remaining chocolate mixture. Beat in the remaining flour mixture until just incorporated.
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6
Divide the batter (using a 1 cup measure) and evenly pour into the prepared pans, smoothing the surface with a spatula. Bake 13 to 15 minutes or until a toothpick inserted into the cake comes out clean.
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7
Place the cakes (in the pans) on a wire rack to cool. Then invert the cakes onto a greased rack. Cool completely before frosting.
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8
To prepare the buttercream, put egg whites and sugar in a mixing bowl over a pot of simmering water. Use an electric hand mixer to beat constantly until the sugar has completely dissolved and the egg whites are hot. Remove from heat.
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9
With whisk attachment, continue whipping the mixture in a standing mixer until thick, glossy, and cool.
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10
Switch over to the paddle attachment. While mixing on medium speed, continuously add chunks of the softened butter until fully incorporated. Continue to mix until it has reached a silky smooth texture. If it curdles, keep mixing and it will come back to smooth. Add vanilla and salt and mix well.
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11
Right before frosting the cake, add the espresso into the buttercream and beat for another 10 seconds. Reserve 1 cup of buttercream for piping on top.
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12
To assemble the cake, place one cake layer on your serving plate and spread with 1/3 cup of the buttercream. Repeat this process until all cake layers are placed. Smear buttercream on top and sides of the cake. Garnish with the sliced almonds.
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13
Use a large star tip to pipe a decorative border on the top edge of the cake.
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14
Cover and refrigerate the cake. Leave out in room temperature for at least an hour prior to serving.
