Mix: In a large mixing bowl, combine the diced potatoes, onion, cream of chicken soup, cheddar cheese soup, sour cream, and ham.
Season: Add salt and black pepper to taste. Mix thoroughly until all potato and ham pieces are evenly coated in the sauce.
Assemble: Transfer the mixture into a 7x13 inch baking dish, spreading it out into an even layer.
Top: Sprinkle the shredded cheddar cheese evenly over the top of the mixture.
Bake: Bake at 350°F (175°C) for 45–55 minutes. The casserole is done when the sauce is bubbly and the potatoes are fork-tender.
Rest: Let the casserole sit for 5 minutes before serving to allow the sauce to set slightly.