Preheat oven to 350. Grease and lightly flour 9-inch springform pan.
In large mixer bowl, cream butter (1/2 cup plus one tbsp) with sugar until light and fluffy, about five minutes. Add egg yolks and beat just until combined. Add melted chocolate and mix just until blended.
In another bowl beat egg whites until stiff peaks form. Fold into chocolate mixture. Turn into prepared pan. Bake 40 minutes or until center springs back when gently touched. Place on wire rack; remove sides of pan. Cool to room temperature. Spread preserves over top of cake, then top with chocolate curls. Serve with sweetened whipped cream.
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