Chocolate Truffle Cake

Heat oven to 425°F (220°C). Grease bottom of 9-inch springform pan. In a medium microwave-safe bowl melt butter; add 3/4 cup cocoa and 1 cup sugar, stirring until well blended. Cool 5 minutes. With wooden spoon, stir in flour and vanilla; add egg yolks, one at a time, beating well after each addition. Beat egg whites with remaining 1 tablespoon sugar in medium bowl until soft peaks form; gradually fold into chocolate mixture. Spoon batter into prepared pan. Bake 15 to 18 minutes or just until edges are firm (center will be soft). With spatula, loosen cake from side of pan. Cool completely on wire rack; remove side of pan. Cover; refrigerate at least 6 hours. Serve cake with sweetened whipped cream or vanilla ice cream, if desired.