Makes one 9-inch cake
Butter (for the pan)
Flour (for the pan)
1 1/4 cups walnut pieces
1 tablespoon unsweetened Dutch-processed cocoa powder
8 ounces bittersweet or semisweet chocolate, coarsely chopped
3/4 cup (1 1/2 sticks) unsalted butter, cut up
6 eggs, separated
3/4 cup light brown sugar
1 tablespoon dark rum or grappa
1/2 teaspoon kosher salt, plus a pinch for the whites
1 tablespoon plus 1 teaspoon granulated sugar
1. Set the oven at 350 degrees. Lightly butter a 9-inch springform pan, dust it with flour, tapping out the excess.
2. Set the walnuts on a rimmed baking sheet and toast them in the oven for 12 minutes or until they are golden. Leave to cool. Leave the oven on.
3. In a food processor, combine the walnuts and cocoa powder. Pulse until the nuts are finely ground.
4. In a large heatproof bowl over a pan of simmering water, combine the chocolate and butter. Stir often until the mixture melts. Remove the bowl from the heat and let it cool to lukewarm.
5. In an electric mixer fitted with the paddle attachment, if you have one, or the whisk, beat the egg yolks with the brown sugar at medium speed for 3 minutes or until the mixture is thick and pale in color. Beat in the rum or grappa with 1/2 teaspoon salt. Using a spatula, fold the egg mixture into the melted chocolate mixture. Fold in the nuts and cocoa.
6. Rinse and dry the mixer bowl. Place the whites with the pinch of salt in the bowl. With the whisk attachment, beat the whites on medium speed for 2 minutes or until they are thick but not peaking. Continue beating while you add the granulated sugar gradually. Turn the speed to high and beat the whites for 1 minute or until they peak softly.
7. Fold the whites into the cake batter, transfer to the pan, smooth the top, and set in the center of the oven. Bake the cake for 40 to 45 minutes or until it is puffed and just beginning to crack. Turn the cake around halfway through baking so it cooks evenly.
8. Let the cake cool in the pan for 20 minutes, then unlatch the sides of the springform and let the cake cool completely. The center may sink a little.
9. Carefully transfer the cake to a serving plate. Adapted from "Dolce Italiano"