Chocolate Volcano Cakes

Preheat oven to 350°F (180°C).

Line small baking sheet with plastic wrap; set aside.

Ganache: Place chocolate in bowl. In small saucepan, heat cream over medium heat just until steaming and bubbles form around side of pan. Pour over chocolate, whisking just until melted. Refrigerate, stirring often, for 30 minutes or until think enough to hold shape. Spoon ganache onto prepared pan in 6 mounds, each about 1 1/2 inches (4 cm) high. Cover loosely with plastic wrap and freeze for at least 4 hours or until firm. (Make ahead: Freeze for up to 1 week.)

Generously grease six 3/4-cup (175 mL) soufflé dishes or ramekins. Line bottoms with parchment or waxed paper. Set aside.

In large heatproof bowl set over hot (not boiling) water, melt chocolate with butter, stirring. Remove bowl and let cool for 30 minutes or until at room temperature. Beat in 1/3 cup (175 mL) of the sugar and vanilla. Beat in eggs yolks, 1 at a time and scraping down bowl after each addition, until slightly thickened.

In separate bowl and using clean beaters, beat egg whites with cream of tartar until soft peaks form. Beat in remaining sugar in thin steady stream until stiff peaks form. Fold one-third each of egg white mixture and flour into chocolate mixture just until blended; repeat twice. Divide half among prepared dishes; place frozen ganache mound in centre of each. Cover with remaining batter, smoothing top. (Make-ahead: Cover with plastic wrap and refrigerate for up to 8 hours.)

Bake on baking sheet in centre of oven for 22 minutes or until top is puffed and edge is set but centre is still soft. Let cool on rack for 2 minutes. With fingertips or knife, gently loosen from dishes. Unmould onto dessert plates. Serve immediately.