1 1/2 c. unsalted butter
Chocolate curls (optional)
4 eggs, separated
3/4 c. unsweetened cocoa
1 c. sugar
1 c. chilled heavy cream
2 tsp. vanilla
1 tbsp. flour
1 tbsp. sugar

Preheat oven to 425 degrees. Grease bottom of 8-inch springform pan. In medium saucepan over low heat, melt butter. Add 1 cup sugar and cocoa, stirring until well blended. Remove from heat; cool slightly. Stir in flour and vanilla.

With electric mixer at medium speed, add egg yolks, one at a time, beating well after each addition. Wash beaters.

In small bowl with mixer at high speed, beat egg whites with remaining 1 tablespoon sugar until soft peaks form. With rubber spatula, gradually fold into chocolate mixture. Spoon batter into prepared pan. Bake 16-18 minutes or until edges are firm (center will be soft).

Remove to wire rack to cool completely. (Cake will sink slightly in center as it cools). Remove sides of pan. Refrigerate cake at least 6 hours. (Remove bottom of pan before icing.)

In small bowl with electric mixer, beat cream until soft peaks form. Spread very thick layer of whipped cream over sunken top of cake. Garnish with chocolate curls. Cut cake while cold, but let stand at room temperature, 10 to 15 minutes before serving.