Combine potatoes, ham, corn and parsley; set aside. For the sauce, I cooked 1/4 cup chopped onions and two stalks of celery (sliced) in the 1/4 cup butter. To that, I added 1/3 cup of flour, 2 cups of milk, a few good shakes of pepper, maybe 1 minced clove of garlic powder and ½ tsp of cayenne. I also added around a cup or so of shredded cheddar to make it a nice tasty cheese sauce.
I mixed the sauce with the other ingredients, poured into a greased 9x13 dish, and topped with another 1½ cups of cheddar