Put water in bowl of food processor, sprinkle gelatin over water and soak 10 minutes. Heat lemon juice, turn on processor, add lemon juice, and turn off. Add sugar, egg yolks and vanilla; process 5 minutes. Scrape sides; let mixture cool. Whip cream; fold into lemon mixture. Beat egg white until stiff but not dry. Fold into mixture. Pile into 1-quart souffle dish with a waxed paper collar held on with masking tape. Smooth top. Refrigerate at least 4 hours or overnight. To serve, carefully remove collar, decorate with Whipped cream rosettes around edge of top and in center. Garnish with a twisted lemon slice and mint leaves if desired.