The most important thing for this recipe is to parboil the potatoes before hand.
It shortens the cooking time if you need it ready in less than 40 minutes!
"Vienna" Billy Joel
Preheat oven to 350°F. Butter a large casserole dish with 1 1/2 Tbsp of butter. If you use a casserole dish that is about 9x13 you'll have more surface area, more of the potatoes will brown, and the cooking time will be faster.
Cover the casserole with aluminum foil and bake in the oven for one hour. After an hour, remove from the oven, remove the foil, sprinkle on the remaining Swiss and Parmesan cheese. Return to the oven for an additional 30-40 minutes. When done, the potatoes should be tender, but not mushy, and the liquid should be mostly absorbed.