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1
Preheat oven to 350 F. Grease three 9-inch round cake pans, and line the bottoms with a circle of parchment paper. Set pans 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 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 into three equal parts and pour into the prepared pans, smoothing the surface with a spatula. Bake 20 to 25 minutes or until a toothpick inserted into the center of a cake comes out clean.
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7
Place the cakes (still 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 frosting, put the butter into a mixing bowl. Beat butter for a few minutes with a mixer using the paddle attachment on medium speed. Add powdered sugar and turn your mixer on the lowest speed until the sugar has been incorporated with the butter. Increase mixer speed to medium and add vanilla extract, blueberry puree, lemon zest and cream. Then beat for another 3 minutes.
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9
To assemble the cake, place one cake layer on your serving plate and spread with 1/3 cup frosting. Place another cake layer on top, and gently press down a little bit. Spread with another 1/3 cup of frosting. Place the last layer of cake on top, smear the remaining frosting on the top and sides of the cake.
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10
Pipe any additional frosting on top of the cake and garnish with blueberries if desired.
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11
Cover and refrigerate. Remove from refrigerator an hour before serving.
