Optional fruit toppings: mandarin oranges, sliced fresh strawberries and sliced kiwifruit
In a large microwave-safe bowl, combine sugar and cornstarch. In a small bowl, combine the egg yolks, orange juice, milk and lemon juice; stir into sugar mixture until smooth.
Microwave on high for 5-7 minutes or just until mixture reaches 160°, stirring every minute. Cool to room temperature; press plastic wrap onto surface of custard. Refrigerate until chilled.
Fold in sour cream; pour filling into crust. Cover and chill for at least 4 hours or overnight.
Just before serving, in a large bowl, beat cream until it begins to thicken. Add confectioners' sugar and vanilla; beat until stiff peaks form. Spread over pie. Sprinkle with orange zest; top with fruit if desired.