- 1 1/4 cups cake flour (not self-rising) plus additional for dusting
- 1 1/2 cups granulated sugar
- 6 large eggs, separated
- 2 tablespoons warm water
- 1 teaspoon vanilla
- 4 ounces hazelnuts (1 cup)
- 3 cups chilled heavy cream
- 1/2 cup confectioners sugar
- 1/3 cup Strega liqueur
- 2 ounces fine-quality bittersweet chocolate, shaved
- Preheat oven to 350°F and butter a 10- by 2-inch round cake pan or 10-inch springform pan. Line bottom with a round of wax paper. Butter paper. Dust pan with flour, knocking out excess.
- Sift together 1 1/4 cups flour and 2 tablespoons sugar. Beat together yolks, 1‰ cups sugar, and warm water with an electric mixer until thick, pale, and doubled in volume, 5 to 7 minutes. Beat in vanilla, then gradually beat in flour on low speed until incorporated.
- Beat whites in a large bowl with cleaned beaters until they hold soft peaks. Add remaining 2 tablespoons sugar. Beat until whites just hold stiff peaks. Fold one third of whites into yolk mixture gently but thoroughly. Fold in remaining whites.
- Pour batter into cake pan and bake in middle of oven until pale golden and a tester inserted 1 inch from center comes out with a few crumbs adhering, 30 to 40 minutes. Turn off oven and cool cake in oven with door ajar 30 minutes. Run a knife around edge of cake and invert onto a rack. Remove pan and paper, then cool completely.
- Preheat oven to 350°F.
- Toast hazelnuts in a baking pan in middle of oven until golden and skins are blistered, 10 to 15 minutes. Wrap nuts in a kitchen towel and let them steam 1 minute. Rub nuts in towel to remove loose skins (don't worry about skins that don’t come off).
- Grind warm nuts in a food processor until they form a paste and chill until cold.
- Beat 2 cups cream with 5 tablespoons confectioners sugar with electric mixer until it holds stiff peaks. Chill until ready to assemble cake.
- Beat remaining cup cream with remaining 3 tablespoons confectioners sugar until cream just holds stiff peaks, then beat in cold hazelnut paste. Chill hazelnut filling until ready to assemble cake.
- Trim off any loose, crusty pieces from top and sides of cake. Halve cake horizontally with a long serrated knife and remove top half. Brush bottom half with two thirds of Strega, then spread all of hazelnut filling over it. Cover with top half of cake and brush with remaining Strega. Frost side and top of cake with whipped cream.
- Freeze cake until firm, at least 3 hours. Let cake stand at room temperature 1 hour before serving, then sprinkle top with chocolate shavings.