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1
Preheat oven to 350u00b0F. Grease three 9-inch round cake pans and line the bottoms with parchment paper.
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2
In a large bowl, whisk the flour, baking powder, baking soda and salt.
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3
In another bowl, whisk the boiling water and cocoa powder until smooth.
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4
Beat butter and sugar together on medium speed in a 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 chocolate 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 and pour into the prepared pans, smoothing the surface with a spatula. Bake 20 to 25 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 frosting, put sugar and egg whites 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 a 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 softened butter in chunks until incorporated, and mix until it has reached a silky smooth texture. If it curdles, keep mixing and it will become smooth again. Add vanilla and salt, mix well.
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11
Equally split buttercream into 3 portions. Mix one of the portions with melted chocolate, and another portion with strawberry puree until incorporated and colors are even.
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12
To assemble the cake, place one cake layer on the serving plate and spread with chocolate buttercream. Place another cake layer on top, and gently press down a little bit. Spread with vanilla buttercream. Place the last layer of cake on top. Gently press down and smear the strawberry buttercream on top.
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13
Carefully smear the side with the extra buttercream squeezed out between cake layers, and form the rustic striped effect.
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14
Cover and refrigerate the cake. Leave out at room temperature for at least an hour prior to serving.
