Blueberry Buttermilk Sherbet

2 cups fresh or unsweetened frozen blueberries
2 teaspoons grated lemon zest
2 Tablespoons lemon juice
1/4 cup sugar
1 cup low-fat buttermilk

Rinse and drain blueberries; put in a 2- to 3-quart pan. Add lemon zest, lemon juice and sugar. Stir often over medium-high heat until simmering and blueberries begin to pop, about 6 minutes. Chill until cool or up until next day.

In a blender or food processor, puree the mixture with buttermilk until smooth.

Pour mixture into a 9- to 10-inch square metal pan. Cover and freeze until solid, at least 4 hours. Break mixture into chunks; whirl in a food processor or beat with a mixer until smooth. Return to pan. Cover and freeze until ready to use, within 30 minutes or up to 1 week.

Let hard-frozen sherbet soften slightly before serving.

Makes about 3 cups; 6 servings