Combine egg yolks, 1/4 cup sugar, lemon juice, and lemon rind in a small heavy saucepan or double boiler.

Whisk the mixture over low heat until it becomes creamy and slightly thickened.

Remove from heat and let cool completely.

In a separate bowl, beat egg whites until soft peaks form.

Gradually add the remaining 1/4 cup sugar and continue beating until stiff peaks form.

Gently fold the beaten egg whites into the cooled lemon mixture.

Whip the cream until stiff peaks form.

Gently fold the whipped cream into the lemon-egg mixture.

Sprinkle a thin layer of vanilla wafer crumbs into the bottom of a pan or individual baking cups.

Pour the lemon mousse mixture over the crumbs.

Freeze the mousse until firm, approximately 2-3 hours.

To serve, unmold individual mousses or cut the mousse into squares.