Make this ahead, store it in the freezer and pull out to serve at the last minute. If desired, garnish with fresh raspberries and a dollop of whipped cream.
Lightly butter the base of a 9-inch (2.5 L) springform pan; set aside. In medium bowl, combine Oreo crumbs and butter until moistened. Press evenly and firmly in bottom of pan. Place in freezer.
In heatproof bowl, whisk together egg yolks, 1/2 cup (125 mL) sugar, lemon rind and lemon juice. Place over simmering water and cook, whisking constantly, until translucent and thick enough to coat the back of a spoon, about 5 to 8 minutes. Remove from heat. Whisk raspberry purée into egg mixture, cover loosely and refrigerate until cold, about 30 minutes.
In a clean medium bowl, using an electric mixer, beat egg whites, salt and cream of tartar until foamy; beat in remaining 1/4 cup (50 mL) sugar, 1 tbsp (15 mL) at a time, until stiff peaks form. Gently fold egg whites into raspberry mixture.
In a separate bowl, using electric mixer, whip cream until firm peaks form. Fold into raspberry mixture. Spread filling over crust. Cover with foil and freeze for at least 8 hours or overnight.
Thirty minutes before serving, remove springform ring and place mousse on large plate. Place in refrigerator to soften before cutting into wedges.
- Wrap mousse in springform pan well in plastic wrap, then in foil and freeze for up to 2 weeks
- A serrated knife works well to cut. Run under hot water and wipe with a warm, damp cloth, as needed between cuts, to help keep slices neat and tidy.
- Make individual mousses by spooning filling mixture into small dishes, such as ramekins or into paper lines muffin pan.
- Omit lemon rind and replace lemon juice with milk or water for a nin-citrus variation.