Sam stopped eating most meat when he was about three. From the time he was seven or eight, he ate no meat, fish, or chicken. For many years, he also eschewed most vegetables. This meant that he ate massive amounts of bread, cheese, pasta and potatoes in many formats--pizzas, enchiladas, quesadillas, etc.
One of his favorites, an accompaniment to many family meals (I rarely made whole vegetarian dinners—just added another dish that he would eat), was this mashed potato pie:
Wash four large Russet or Idaho potatoes. Perforate them a few times with a fork or sharp small knife. Rub with olive oil and bake for about an hour at 350 degrees (depending on size).
When they are suitably soft--scoop out the innards--mash them with warm milk, butter, salt and pepper-- (quantities very flexible here--you can also add cheese--parmesan, cheddar, etc.).
Line a ten inch pie pan with the skins. It can all be pretty ragged--you're just serving it out of this dish--so you don't need a perfect "crust." Cover the skins with the newly mashed potatoes--sprinkle more cheese on top--and pop back into the oven. If you've moved quickly--everything should be pretty warm and not need much heating. Before serving slip under the broiler--to get those little swirls of potato and cheese nicely browned.
This, of course, isn't much different from a standard "twice-baked potato," but it is easier to make for a crowd. In any case--endless variations in both shape and addition of all sorts of ingredients-- are obviously possible.