Take 3 of the medium potatoes and cube them. Boil in water til tender. Remove from heat and mash. Add 3T butter and 1/4C milk for mashed potatoes. Salt and pepper to taste. Spread this on the bottom of a 2qt casserole dish.
Take onion, bell pepper and jalepenos. Dice them up. Melt rest of butter in saute pan. Saute veggies til tender. Pour all of it, butter included, on top of mashed potatoes.
Spread MW evenly all over.
Layer with about 1/2C cheese. Sprinkle with seasonings.
Slice remaining potatoes thin. Lay them on top of the dish so far. Pour in 1/2C milk, or until it touches bottom of potatoes. Top with remaining cheese. Then sprinkle with seasonings. Place in oven on 350 for about 1hr, til potatoes are tender.