Puree 2 1/2 cups raspberries, powdered sugar, and kirsch in blender until smooth. Transfer to large bowl.
Using electric mixer, beat cream in another large bowl until firm peaks form. Add sour cream and beat just to blend.
Fold whipped cream mixture into raspberry puree just until incorporated.
Divide mousse among six 6-ounce parfait glasses. Cover each with plastic wrap and freeze. About 2 hours before serving, place mousse in refrigerator to thaw slightly. Uncover mousse and top with remaining 1/2 cup raspberries. Garnish with mint sprigs and serve.
