Bring fresh basil leaves and 1 quart water to a boil over medium-high heat in a medium saucepan. Boil 7 to 8 minutes or until leaves darken; stir in 3/4 cup sugar. Cook, stirring constantly, 2 minutes or until sugar dissolves; remove from heat. Stir in 3/4 cup lemonade concentrate, and let mixture stand 30 minutes.
Pour lemon-basil mixture through a wire-mesh strainer into a large zip-top plastic freezer bag; discard basil leaves. Seal and freeze 8 hours or until mixture is firm. Remove lemonade mixture from freezer, and let stand, turning bag occasionally, 30 minutes or until slushy. Serve with fresh raspberries, if desired.
*Limeade concentrate may be substituted for lemonade concentrate.