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1
350 degrees. Grease 3 (8-inch) round pans, line the bottoms with parchment paper and grease the paper. Use a little cocoa powder to coat the insides of the pans, then tap out excess.
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2
Whisk together cocoa powder and 2/3 cup boiling water. Whisk in milk. In a separate bowl, whisk together cake flour, baking soda, baking powder and salt.
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3
In a large mixing bowl with the paddle attachment, beat butter and sugar until fluffy. Beat in eggs 1 at a time. Beat in vanilla. With the mixer running on low, beat in a third of the dry ingredients, followed by half the cocoa mixture. Add remaining portions, alternating between two mixtures. Beat until smooth.
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4
Divide batter evenly among pans. Bake until the centers of the cakes are firm to the touch, 30 to 40 minutes. Cool cakes on a wire rack for 10 minutes; turn them out onto the rack to cool completely.
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5
Make the buttercream: Fill a medium pot halfway with water and bring to a simmer. In a heatproof bowl that fits over pot, whisk together egg whites, sugar and salt. Cook, whisking constantly, until the sugar dissolves and mixture reaches 140 degrees on a candy or instant-read thermometer, about 5 minutes.
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6
Using an electric mixer, whip until completely cooled and thick, about 5 minutes. Beat in butter a little at a time, until the frosting is smooth and spreadable. Beat in vanilla bean seeds and pepper.
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7
Slice each cake in half horizontally. Place one bottom layer on a large platter or cake stand. Top evenly with a thin layer of buttercream. Repeat, ending with a layer of cake.
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8
Make the frosting: In a medium saucepan over medium heat, combine sugar, heavy cream and salt. Simmer, stirring occasionally, until sugar completely dissolves, about 5 minutes. Scrape mixture into a bowl. Stir in chocolate, butter and vanilla until smooth. Set bowl over a larger bowl filled with ice. Use a hand mixer or an immersion blender with the whisk attachment to whip until mixture is thick and cool, about 5 minutes. Spread frosting.
