Preparation If using ramekins, line each with plastic wrap, allowing a 2-inch overhang. In a very small bowl sprinkle gelatin over cold water to soften. In a bowl with a fork beat yolks until smooth. In a saucepan simmer zest, lemon juice, and 1/3 cup sugar over moderate heat, stirring, until sugar is dissolved and whisk half of lemon mixture in a slow stream into yolks. Transfer yolk mixture to remaining lemon mixture and cook over moderate heat, stirring constantly, until it is thickened and just begins to simmer. Pour mixture through a fine sieve into a large bowl and add gelatin mixture and vanilla, stirring until gelatin is dissolved. Cool lemon mixture to room temperature. In a bowl with an electric mixer beat together whites (or reconstituted dried egg whites) and cream of tartar until meringue just holds soft peaks. Gradually beat in remaining 1/3 cup sugar until meringue just holds stiff peaks. In a bowl with electric mixer beat cream until it just holds stiff peaks. Stir one third meringue into lemon mixture to lighten and fold in remaining meringue and whipped cream gently but thoroughly. Spoon mousse into foil molds or lined ramekins. Chill mousses until set, about 4 hours, and freeze set mousses, covered with plastic wrap, until frozen, about 4 hours, and up to 2 days. Assemble desserts: Spoon some sauce onto 4 dessert plates, tilting plates to coat. If using foil molds, cut tape on cylinders and gently unwrap mousses, arranging 1 on each plate. If using ramekins, remove mousses, using plastic wrap overhang to lift them out, and invert onto plates. Gently remove plastic wrap. Garnish desserts with mint. To Make Foil Molds for Mousses: Tear off 4 12- by 8-inch sheets of foil. Fold each sheet lengthwise into a 12- by 2 1/4-inch strip (about 3 layers thick) and trim each strip to 10 inches in length. Wrap 1 strip, smooth side in, around base of a bottle or glass that is 2 1/4 to 2 1/2 inches in diameter and tape overlapping end of strip at top and bottom of cylinder. Gently slide cylinder off bottle or glass. Create 3 more cylinders with remaining foil strips in same manner. On a small baking sheet stand cylinders on 1 end and tape each to baking sheet in 2 places to prevent them from moving while being filled.
Preparation If using ramekins, line each with plastic wrap, allowing a 2-inch overhang. In a very small bowl sprinkle gelatin over cold water to soften. In a bowl with a fork beat yolks until smooth. In a saucepan simmer zest, lemon juice, and 1/3 cup sugar over moderate heat, stirring, until sugar is dissolved and whisk half of lemon mixture in a slow stream into yolks. Transfer yolk mixture to remaining lemon mixture and cook over moderate heat, stirring constantly, until it is thickened and just begins to simmer. Pour mixture through a fine sieve into a large bowl and add gelatin mixture and vanilla, stirring until gelatin is dissolved. Cool lemon mixture to room temperature. In a bowl with an electric mixer beat together whites (or reconstituted dried egg whites) and cream of tartar until meringue just holds soft peaks. Gradually beat in remaining 1/3 cup sugar until meringue just holds stiff peaks. In a bowl with electric mixer beat cream until it just holds stiff peaks. Stir one third meringue into lemon mixture to lighten and fold in remaining meringue and whipped cream gently but thoroughly. Spoon mousse into foil molds or lined ramekins. Chill mousses until set, about 4 hours, and freeze set mousses, covered with plastic wrap, until frozen, about 4 hours, and up to 2 days. Assemble desserts: Spoon some sauce onto 4 dessert plates, tilting plates to coat. If using foil molds, cut tape on cylinders and gently unwrap mousses, arranging 1 on each plate. If using ramekins, remove mousses, using plastic wrap overhang to lift them out, and invert onto plates. Gently remove plastic wrap. Garnish desserts with mint. To Make Foil Molds for Mousses: Tear off 4 12- by 8-inch sheets of foil. Fold each sheet lengthwise into a 12- by 2 1/4-inch strip (about 3 layers thick) and trim each strip to 10 inches in length. Wrap 1 strip, smooth side in, around base of a bottle or glass that is 2 1/4 to 2 1/2 inches in diameter and tape overlapping end of strip at top and bottom of cylinder. Gently slide cylinder off bottle or glass. Create 3 more cylinders with remaining foil strips in same manner. On a small baking sheet stand cylinders on 1 end and tape each to baking sheet in 2 places to prevent them from moving while being filled.