This is another recipe from Alice Medrich from her Cocolat book:
1 3/4-2 1/4 teaspoons unflavored gelatin (use higher amount when using a mold)
1/2 cup fresh lemon juice
Grated zest of 1 lemon
1 cup of sugar
4 large eggs, separated
1 teaspoon vanilla extract
1/4 teaspoon cream of tartar
1 cup heavy cream
Sprinkle gelatin over 3 teasponns of cold water in small container. Set aside for 5 minutes without stirring.
Bring lemon juice, zest and 1/2 cup sugar to a simmer over a nonreactive pan.
PLace egg yolks in small bowl and pour hot lemon mixture over them, whisking constantly to prevent scoarching. Return mixture to pan and cook over low heat stirring constantly to prevent sticking and scoarching. Cook until it begins to simmer and remove from heat. Pour through a strainer into a clean bowl. Whisk in softened gelatin and vanilla. Let cool to room temperature.
In a clean dry mixing bowl whisk egg whites and cream of tartar on medium speed until soft peaks form. Gradually add remaining 1/2 cup sugar while mixing. Beat at high speed until stiff but not dry.
Fold 1/4 beaten egg white into lemon mixture to lighten.
Immediately beat cream in same bowl as egg whites until soft peaks form. DO NOT OVERBEAT or mousse will be grainy. Fold beaten cream and the rest of egg whites into lightened lemon mixture.
Turn mousse immediately into a mold or serving glasses. Cover and refrigerate for at least 4 hours.
Copyright (c) 1990 Alice Medrich