For the cake: Preheat the oven to 350 degrees F. Grease two 9-by-2-inch round cake pans; dust the pans with flour, and knock out excess.
In a large measuring cup, combine the buttermilk, coffee, vanilla and 1 1/2 cups water. In a stand mixer fitted with the paddle attachment, add the sugar, flour, cocoa powder, baking powder, baking soda and salt. Mix on low speed. Mix in the butter and eggs, and then slowly add the buttermilk mixture, scraping down the sides of the bowl as needed.
Divide the batter evenly between the prepared cake pans. Bake until the cake layers begin to pull away from sides of the pan and a toothpick inserted into center comes out clean, 22 to 25 minutes.
For the Swiss meringue buttercream: Add the sugar and egg whites to a heatproof stand mixer bowl, and set over a pan of simmering water. Whisking constantly, heat until the sugar is dissolved and the mixture registers 160 degrees F on an instant-read thermometer. Transfer the bowl to the stand mixer fitted with the whisk attachment, and beat on medium-high speed until fluffy and cooled, about 10 minutes. Continue beating until stiff, glossy peaks form. Reduce the speed to medium-low and add the butter, 1 tablespoon at a time, beating well after each addition. Add the vanilla. (Makes 7 cups. See Cook's Note.)
For the raspberry buttercream: In a stand mixer fitted with paddle attachment, beat 800 grams of the Swiss meringue buttercream together with the raspberry puree until fully incorporated. (Makes 4 cups.)
To assemble: Level and tort both cakes--you will end up with 4 layers of cake. Place one cake layer on a serving platter; add about a 1/2-inch layer of the raspberry buttercream. Repeat until you have 4 stacked layers of cake and 3 layers of filling. Frost the cake with the remaining Swiss meringue buttercream.
The Swiss meringue buttercream can be refrigerated in an airtight container for up to 3 days, or frozen up to 1 month. Bring to room temperature before using, and beat on the lowest speed until smooth, about 3 minutes.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.