1.) In a small saucepan, combine the sugar, water, and fresh mint leaves. Allow the mixture to simmer over medium/ low heat for about 10 minutes, stirring occasionally. Do not let the sugar burn! Strain into a freezer-friendly container that seals (i.e., Tupperware) and discard the mint leaves. Seal the container and place in the refrigerator for about a half-hour to cool.
2.) While the mint syrup cools, make the grapefruit cups: Cut the two grapefruit into halves. Cut around each half, loosening the flesh from the outer skin, being careful to preserve hemisphere shape. The shells will be used as cups later. Remove the fruit from the peel with a grapefruit spoon or the like. Cover the shells and set aside in the refrigerator.
3.) Now make the grapefruit juice. Either run the grapefruit flesh through a juicer machine, or just squeeze the juice out with your hands. Add the juice to the cooled mint syrup, and beat together with a whisk.
4.) Place the mixture in freezer-friendly container into the freezer for about 3 hours, or until semi-firm (not solid). Remove from the freezer and place semi-solid mixture into the blender. Blend until smooth and slushy.
5.) Spoon the frozen sorbetto (slush) into the grapefruit shells. Cover and freeze until solid, 5 hours or overnight.
6.) Yummy!