Flourless Chocolate Cake with Chocolate Ganache

Butter a 9-inch springform pan; line bottom of pan with parchment or waxed paper. Butter the paper. Wrap outside of pan with foil.

Stir 12 ounces chocolate and 3/4 cup butter in medium saucepan over low heat until melted and smooth; remove from heat. Cool to lukewarm, stirring often.

Using an electric mixer, beat egg yolks and 6 tablespoons sweetener in a large bowl until thick and pale yellow, about 3 minutes.

Fold lukewarm chocolate mixture into yolk mixture. Fold in vanilla.

Using clean, dry beaters, beat egg whites in another bowl until soft peaks form. Gradually add remaining 6 tablespoons sweetener beating until stiff peaks form.

Fold whites into chocolate mixture in three additions; pour batter into prepared pan.

Bake cake until top is puffed and cracked and tester inserted into center comes out with moist crumbs attached, about 50 minutes. Cool cake in pan on rack (cake will fall).

Cut around pan sides to loosen cake and remove pan sides. Place a 9-inch tart pan bottom or cardboard round on top of cake and invert cake; remove parchment.

To make ganache, bring whipping cream to a boil; remove from heat just when it is about to boil over. Add 9 ounces chocolate and whisk until melted and smooth. Place cake on rack over baking sheet to catch ganache drips.

Spread 1/2 cup ganache over top and sides of cake; freeze until almost set, about 4 minutes. Pour remaining ganache over cake; smooth top and sides. Place cake on platter; chill until firm.

Garnish with chocolate shavings and serve at room temperature.