1. Place the ricotta, lemon zest, lemon juice, cream and powdered sugar in the bowl fitted with the whisk. Mix at speed 6 for 1 minute. Pour mixture into ice cube trays. Freeze for 2-3 hours or until completely frozen. For longer storage, cover trays with plastic wrap.
2. When cubes are completely frozen, place Prep&Cook bowl in the freezer for 5 minutes to chill. Remove 1 tray of cubes and place in the chilled bowl fitted with the kneading/crushing blade. Pulse for 1 minute 30 seconds. Scrape down the sides of the bowl. Add one egg white and mix at speed 12 for 30 seconds.
3. Repeat step 2 with the remaining frozen cubes and egg white. Serve immediately