Rich and totally indulgent.
6 tablespoons butter, plus more for pan
8 ounces bittersweet or semisweet chocolate, finely chopped
6 large eggs, separated
1/2 cup granulated sugar
1/2 teaspoon salt
Confectioners' sugar, for dusting
Sweetened whipped cream, for serving
Preheat the oven to 275 degrees with the rack in the center. Butter the bottom and sides of a 9-inch springform pan. Place butter and chocolate in a large heatproof bowl and microwave in 30-second increments, stirring each time, until completely melted. Add salt.Let cool slightly. Whisk in egg yolks.
In a large bowl, beat egg whites until soft peaks form.Gradually add granulated sugar, and continue beating until glossy stiff peaks form.
Whisk 1/4 of the egg whites into the chocolate mixture; then gently fold in remaining egg whites.
Pour batter into the prepared pan, and smooth the top with a rubber spatula.
Bake until the cake pulls away from the sides of the pan and is set in the center, 45 to 50 minutes. Cool completely on a wire rack; remove sides of pan. Serve at room temperature, dusted with confectioners' sugar.
Serve with whipped cream or ice cream, if desired