RECIPE INGREDIENTS (Serves 8):
2/3 cup hazelnuts, 3 oz.
5 oz. dark chocolate, broken into pieces
5 Tablespoons unsalted butter
2/3 cup sugar
4 large eggs, separated
3/4 cup all-purpose flour
a pinch of salt
1/4 cup sour cream or crème fraîche
whipped cream or crème fraîche, sweetened, to serve
2 oz. dark chocolate, in one piece
1 tablespoon confectioner's sugar
1 tablespoon cocoa powder
a cake pan, 10 inches diameter, greased
Put all but 2 tablespoons of the hazelnuts in a small food processor and grind to a powder. Set aside.
Put the chocolate and butter in a glass bowl and microwave on HIGH for about 1-1/2 minutes until almost completely melted.
Stir, then let stand until fully melted.
Reserve 1 tablespoon of sugar and put the remainder in a large bowl. Add the egg yolks, then beat until fluffy and lemon-colored. Stir in the chocolate mixture, flour,salt, ground hazelnuts, and sour cream. The mixture will be slightly stiff.
Put the egg whites in another clean, grease-free bowl and beat with an electric hand mixer until frothy. Add the reserved 1 tablespoon sugar and beat on high until they hold stiff peaks. Using a rubber spatula, fold one-third of the egg whites into the chocolate mixture. Add the remaining whites, folding just until there are no more specks of white.
Transfer to the prepared cake pan and bake in a preheated oven at 350°F until knife inserted in the middle comes out clean, 20-30 minutes. Let cool slightly, then invert onto a wire rack to cool.
To decorate, toast the remaining hazelnuts in a dry skillet, then crush lightly. Microwave the chocolate on HIGH for 30 seconds, then shave off curls with a vegetable peeler. Set aside. Put the confectioner's sugar and cocoa in a strainer and hold it over the cake. Tap the edge of the strainer to release the mixture, moving around the cake to coat. A very light dusting is sufficient. Sprinkle the chocolate and toasted hazelnuts in the center. Serve at room temperature, with lots of sweetened whipped cream or crème fraîche. The cake will keep well for several days in an airtight container.