Place potatoes in a large saucepan and cover with water; bring to a boil over medium-high heat. Cover and cook for 15-20 minutes or until tender; drain.
Transfer to a large bowl; mash potatoes. Beat in the cheese, egg, onion, sour cream, salt and pepper.
Cut a hole in the corner of a pastry bag or heavy-duty plastic bag. Insert large star tip #40
Fill bag with potato mixture. Pipe potatoes into eight mounds on a greased baking sheet. Cover and freeze for up to 1 month.
Place on a microwave-safe plate. Cover with waxed paper; microwave on high for 6 minutes or until heated through.
