Heat 1.25 cups sugar and 1 cup water in a saucepan until all of the sugar dissolves completely; then let it cool.
Squeeze the juice out of 6-8 medium-sized grapefruits.
Mix the cooled sugar syrup into the grapefruit juice in a stainless steel bowl, cover with plastic wrap, and put it in the freezer for 8 hours or overnight.
Take it out and with an electric mixer, beat it until it'a fluffy (not that easy, but possible). Then put it back in the freezer for another 3-4 hours.
Eat it! There is really no better desert after a heavy meal.