-
1
Preheat the oven to 350.
-
2
Butter two 9-inch round cake pans and line the bottoms with parchment paper.
-
3
Butter the parchment and dust with bread crumbs, tapping out any excess.
-
4
In a food processor, pulse the walnuts until finely chopped.
-
5
Add the cocoa powder, cake flour and espresso powder and pulse until the walnuts are finely ground.
-
6
Transfer to a bowl.
-
7
In a large bowl, using an electric mixer, beat the yolks at medium speed until thick and pale, 3 minutes.
-
8
Beat in 2/3 cup of the sugar; increase the speed to high and beat until thick, about 5 minutes.
-
9
Beat in the vanilla.
-
10
In a medium bowl, using clean beaters, beat the egg whites and salt at medium speed until soft peaks form.
-
11
Gradually add the remaining 1/3 cup of sugar and beat at high speed until the whites are stiff and glossy.
-
12
Fold the egg whites and ground walnuts into the yolk mixture in 3 batches; fold just until no streaks remain.
-
13
Divide the batter between the prepared pans; smooth the tops.
-
14
Bake for about 20 minutes, until the cakes are golden and springy.
-
15
Transfer to a rack for 10 minutes, then invert the cakes and cool completely.
-
16
Peel off the parchment; turn the cakes right side up.
-
17
Fill a medium bowl with ice water.
-
18
In a medium heatproof bowl, whisk the yolks, sugar and salt.
-
19
Gradually whisk in the dissolved espresso.
-
20
Place the bowl over a saucepan of barely simmering water and cook, stirring with a spatula, until the yolks are thick enough to coat the spatula and an instant-read thermometer inserted into the mixture registers 175, about 10 minutes.
-
21
Set the bowl in the ice bath and cool, stirring occasionally.
-
22
In a large bowl, using an electric mixer, beat the butter at medium speed until smooth.
-
23
Beat in the yolk mixture in 4 batches, beating well between additions.
-
24
Beat in the liqueur and vanilla.
-
25
Using a serrated knife, split each cake in half horizontally.
-
26
Set a top layer, cut side up, on a cake plate; brush it with 2 tablespoons of the rum and spread with 1/2 cup of the filling.
-
27
Top with a bottom cake layer; brush with 2 more tablespoons of rum and spread with another 1/2 cup of filling.
-
28
Repeat with the remaining top cake layer, ending with the bottom layer, cut side down.
-
29
Brush the top of the cake with the remaining 2 tablespoons of rum and spread the sides of the cake with a thin layer of filling.
-
30
Spread the remaining filling on the top.
-
31
Press the chopped walnuts around the side of the cake.
-
32
Refrigerate the cake for at least 4 hours or overnight.
-
33
Let the cake stand at room temperature for 15 minutes, then scatter the walnut halves on top before serving.
