Scrub potatoes and pat dry. Prick skin of each with a fork. Bake in 400 degrees oven 1 hour or until soft and skins firm. Cut a slice from the top of each, long ways. Carefully, using a spoon, scoop out the pulp, leaving enough for a 1/4-inch thick shell. Put potato pulp in a bowl and mash, beat in enough milk to make smooth and fluffy. Add butter. Stir in cheese, egg, onions, salt and pepper; spoon back into shells, mounding slightly. To serve immediately, place in 350 degrees oven to just heat through for about 10 minutes. To serve later in the day, cover and refrigerate until 30 minutes before serving time. Heat 20-30 minutes at 350 degrees. To freeze, place on baking sheet and freeze 1 hour until firm. Remove and wrap individually.
Ready in 1 ½ hour