Use ONLY instant potatoes!
I have doubled, tripled and quadrupled this recipe without any problems.
Mix instant mashed potatoes according to package directions. I use real butter only and evaporated milk. Allow potatoes to cool slightly (about 15 to 20 minutes.)
While potatoes are cooling, preheat oven to 350 degrees. Grease a 3 quart casserole dish, I like to use a shallow dish.
Beat 3 eggs together in a dish and stir into the mashed potatoes, add a dash of garlic powder, and shredded cheeses. Mix well and pour into baking dish. Bake in oven until puffed, golden brown and set (about 45 minutes.)