Vodka keeps the sherbet from freezing rock hard, but it's optional. For a delicious garnish, boil julienne strips of grapefruit rind in simple syrup for 30 minutes; drain and toss in sugar.
1 cup water
2 tablespoons finely chopped red grapefruit rind
1 cup sugar
1 cup fresh red grapefruit juice
2 cups whole buttermilk
2 tablespoons vodka
How to Make It
Bring 1 cup water to a boil in a small saucepan. Add rind to pan; reduce heat, and simmer for 2 minutes. Drain, reserving rind. Combine rind, sugar, and juice in pan; bring to a boil, stirring constantly until sugar dissolves. Reduce heat, and simmer 20 minutes. Remove from heat; pour into a bowl. Chill for 1 hour. Strain juice mixture, and discard solids. Combine the juice mixture, buttermilk, and vodka in the freezer can of an ice-cream freezer; freeze according to manufacturer's instructions.