4 ounces bittersweet chocolate ( at least 70% cacao)
8 tablespoons unsalted butter
4 large eggs, separated
½ cup sugar plus 2 tablespoons for topping
⅛ teaspoon salt
¼ teaspoon cream of tartar
½ cup chestnut flour
½ cup chopped cooked chestnuts*
1/3 to ½ cup sweetened chestnut purée
1 cup heavy cream, for topping
Chocolate curls or cocoa powder, for garnish
- Heat oven to 375º.
- Melt chocolate and butter in a bowl set over boiling water until chocolate is nearly completely melted, then remove from heat and whisk mixture until smooth.
- In a medium mixing bowl, whisk egg yolks with half the sugar (¼ cup) and the salt until pale and thick. Stir in the warm chocolate and set aside.
- Put egg whites in a clean bowl with cream of tartar and beat until fluffy. Add the remaining ¼ cup sugar and beat until whites are stiff but not dry.
- Stir chestnut flour and chopped chestnuts into the chocolate batter, then fold in ¼ of the whites to lighten mixture. Fold in remaining whites and scrape batter into an unbuttered 8-inch spring-form pan, smoothing top as necessary.
- Bake for 25 to 30 minutes, until a tester inserted in the center of the cake comes out almost clean.
- Cool on a rack. Don’t be alarmed by a bit of sinking or cracking. When cool, run a knife around the edge of cake to free sides then remove form. Transfer to a serving platter.
- Using either a flat knife or a spatula, spread the chestnut puree evenly over the top of the cake.
- To serve, whip cream with 2 tablespoons sugar to a very soft consistency. Spoon over top of cake and quickly spread with a spatula. Sprinkle with chocolate curls or cocoa powder.
*If you don’t have the time to roast and peel the chestnuts, use the vacuum-packed chestnuts.
**Cake may be stored, covered, at room temperature for up to 3 days.