1. Wash and dry the berries. Place on a tray lined with wax paper and freeze for 6 hours.
2. Once frozen, place berries in a bowl fitted with the kneading/crushing blade.
3. Pulse for 1 minute 30 seconds. Scrape down the sides of the bowl. Add powdered sugar and egg whites. Mix at speed 12 for 30 seconds.
4. Serve immediately.