Combine chocolate and water in a glass measuring cup and heat on low setting in the microwave until the chocolate is melted. Stir in the vanilla and cool to room temperature. In a large bowl, beat the cream just until it begins to thicken. Gradually add the sugar and continue beating until it holds a soft shape. Using a spatula, stir about 2 TBS of the whipped cream into the cooled chocolate. Gradually stir in additional 3 TBS of cream until the chocolate is smooth and mounds lightly. Pour the chocolate mixture into the remaining whipped cream. Fold with the spatula until combined and evenly colored.
Pour the chocolate cream mixture into a metal bowl or container (2 quart capacity). Cover the container tightly with foil and freeze for several hours or overnight. To serve, scoop the frozen chocolate cream into glass bowls or footed glasses. Garnish with mint leaves. Makes 2 quarts.