Frozen Lemon Souffle

Line bottom and side of 9-inch (2.5 L) springform pan with plastic wrap; set pan aside.

Crust: In food processor, whirl vanilla wafers into fine crumbs; drizzle in butter, pulsing to moisten. Press over bottom of prepared pan. Set aside.

In heatproof bowl, whisk together egg yolks, 1/4 cup (50 mL) of the sugar and lemon rind and juice. Place over simmering water; cook, stirring frequently, until translucent and thick enough to coat back of spoon, about 6 minutes. Strain into large bowl. Place plastic wrap directly on surface; refrigerate until cold, about 1 hour. (Make-ahead: Refrigerate for up to 3 days.)

In clean bowl, beat together egg whites, salt and cream of tartar until foamy; beat in remaining sugar, 1 tbsp (15 mL) at a time, until stiff peaks form. Set aside.

In separate bowl, whip cream; fold into lemon mixture. Fold in one-third of the whites; fold in remaining whites. Scrape over crust, smoothing top. Cover with foil; freeze for 8 hours. (Make-ahead: Freeze for up to 2 weeks.)

Let soften in refrigerator for 30 minutes before serving in wedges.