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1
Preheat the oven to 325.
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2
Lightly butter a 15-by-17-inch jelly-roll pan with 1-inch sides.
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3
Line the bottom with parchment or wax paper; butter the paper.
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4
Dust the pan with flour, tapping out any excess.
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5
In a medium bowl, sift the flour with the cocoa powder, baking soda and salt.
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6
In a large bowl, using an electric mixer, beat the butter at medium speed until creamy.
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7
Add the sugar and vanilla and beat until fluffy.
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8
Add the eggs, 1 at a time, beating well after each addition.
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9
Scrape down the side and bottom of the bowl.
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10
At low speed, beat in the dry ingredients in 3 batches, alternating with the buttermilk.
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11
Pour the batter into the prepared pan and smooth the surface.
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12
Bake the cake in the middle of the oven for about 35 minutes, or until a toothpick inserted in the center comes out clean.
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13
Let the cake cool completely in the pan.
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14
Refrigerate until chilled, about 2 hours.
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15
Heat the chocolate in a microwave oven until nearly melted.
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16
Let stand for 1 minute, then stir until smooth.
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17
Whisk in the heavy cream and 2 tablespoons of the hazelnut liqueur.
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18
Refrigerate the chocolate filling, stirring occasionally, until slightly firm, about 2 hours.
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19
Run the tip of a paring knife around the side of the cake.
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20
Set a large cookie sheet or cutting board on top and flip.
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21
Remove the pan and peel the paper off the cake.
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22
Using a 6-inch corrugated cardboard round as a template, cut out three 6-inch cake rounds as close together as possible.
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23
Using a 4-inch round cardboard template, cut out 2 rounds of cake; using a 2-inch template, cut out 2 rounds from the remaining cake.
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24
Using an electric mixer, beat the chocolate filling until slightly pale and stiff, about 1 minute.
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25
Set one 6-inch cake round on a 6 1/2-inch cardboard round and brush lightly with some of the hazelnut liqueur.
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26
Spread 1/4 cup of the chocolate filling on the top and cover with another 6-inch cake round.
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27
Brush with hazelnut liqueur and spread another 1/4 cup of the chocolate filling on top.
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28
Cover with the last 6-inch cake round; set aside.
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29
Set one 4-inch cake round on the 4-inch cardboard template and brush with hazelnut liqueur.
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30
Spread 3 tablespoons of the chocolate filling on the top and cover with the second 4-inch cake round; set aside.
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31
Set one 2-inch cake round on the 2-inch template and brush with hazelnut liqueur.
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32
Spread 2 tablespoons of the chocolate filling on top and cover with the second 2-inch cake round.
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33
Refrigerate all 3 layer cakes until thoroughly chilled, at least 2 hours.
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34
Fill a pastry bag fitted with a 1/2-inch star tip with 1 cup of the Vanilla Buttercream.
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35
Pipe a small dollop of buttercream into the center of a lazy Susan and anchor the 6-inch layer cake on it.
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36
Pipe the buttercream around the cake to fill any gaps between the layers.
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37
Using a large offset spatula, spread a very thin layer of buttercream over the entire cake.
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38
Carefully lift the cake off the lazy Susan and refrigerate to set the frosting, about 10 minutes.
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39
Fill in between the layers and frost the 4-inch and 2-inch layer cakes.
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40
Return the 6-inch cake to the lazy Susan and frost with 1 cup of the buttercream.
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41
Run a large offset spatula under hot water, wipe it dry and use it to spread the frosting on the side of the cake in a smooth, even layer.
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42
Insert a plastic straw in the center of the cake and trim the straw flush with the cake.
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43
Refrigerate until chilled, at least 2 hours.
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44
Frost the 4-inch cake with buttercream.
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45
Insert a plastic straw in the center, leaving it protruding.
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46
Refrigerate until firm.
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47
Frost the 2-inch layer cake with buttercream and refrigerate until chilled.
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48
Transfer the 6-inch cake to a cake plate.
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49
Center the 4-inch cake on top, using the straw to help maneuver the cake.
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50
Trim the straw flush with the cake.
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51
Center the 2-inch cake on top.
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52
Fill the pastry bag with the remaining buttercream and pipe a decorative border around the base of each tier, covering the cardboard.
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53
Refrigerate the cake until firm.
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54
Let the cake stand at room temperature for at least 1 hour before serving.
