In a bowl, over a double boiler set to medium heat, cook all ingredients, whisking constantly. Cook until just before boiling. Remove from heat, and allow to cool completely.
When the curd is cool, spread crushed vanilla wafer cookies in bottom of 13 x 9 inch baking dish (reserving 2 tablespoons of crumbs for top).
Beat egg whites until stiff peaks form. Then beat cream with sugar and vanilla until peaks form. Fold beaten egg whites and lemon curd into cream mixture, and combine completely.
Carefully pour filling over crumbs, spread gently so crumbs aren’t displaced, and sprinkle top with remaining crumbs.
Cover tightly with plastic wrap or foil, and freeze for several hours or overnight.