A touch of rosewater, which is available at Middle Eastern markets and specialty food stores, enhances the flavor of the berries. If you can't find it, omit it. Prepare this up to three days ahead.
1 1/2 cups water
1/2 cup sugar
1 pound blackberries (fresh or frozen)
1/4 teaspoon finely grated lemon rind
1 tablespoon fresh lemon juice
1/4 teaspoon rosewater
How to Make It
Combine 1 1/2 cups water and sugar in a small saucepan, and bring to a boil. Cook over medium-high heat for 2 minutes or until sugar dissolves, stirring constantly. Remove from heat; cool. Pour into a blender. Add blackberries and remaining ingredients; process until smooth. Strain mixture through a fine sieve into a bowl, and discard solids. Pour mixture into an 11 x 7-inch baking dish; cover and freeze 45 minutes. Stir blackberry mixture with a fork every 45 minutes until completely frozen and slushy (about 3 hours).
Remove blackberry mixture from freezer; scrape with a fork until fluffy.