Boil potatoes in salted water, until they are tender.
Drain, and let cool to the touch. Using a ricer, rice potatoes into a large bowl.
Mix in remaining ingredients. Add milk a little at the time, and use just enough to make the potatoes loose, but not soupy. Reserve a bit of the butter.
Spoon into a 9X13 casserole dish. Poke holes in the potatoes with the end of a wooden spoon. Pour remaining melted butter into the holes.
Cover tightly and freeze.
Before serving, thaw and bring casserole to room temperature.
Bake at 350` for 30 minutes, or until potatoes are warm through.
You can mix the potatoes and all other ingredients in a mixer on high speed.
I sometimes roast 1-2 heads of garlic, and mash the roasted garlic into the potatoes.