Wash the potatoes thoroughly under cold water, then peel and slice them into thin, even pieces—about an eighth of an inch thick. Next, dice the chicken ham and onion, and mince the garlic.

Lightly grease the inside of your six-quart slow cooker with a tablespoon of melted unsalted butter.

Begin layering by placing one-third of the sliced potatoes across the bottom of the slow cooker. Sprinkle one-third of the diced onion and chicken ham over the potatoes. Add one-third of the shredded cheddar cheese. Repeat this layering process two more times.

In a medium mixing bowl, combine the condensed cream of chicken soup, whole milk, and heavy cream. Pour in the melted butter, and add the minced garlic, salt, black pepper, dried parsley, paprika, dried thyme, and onion powder. Whisk until smooth.

Slowly pour the creamy sauce over the layered potatoes and chicken ham. Cover the slow cooker securely with its lid.

Set your slow cooker to low heat and cook for 5 to 6 hours. Check for doneness by inserting a fork into the center; the potatoes should be completely tender.

Once the potatoes are tender, sprinkle the remaining shredded cheddar cheese evenly over the top. Cover the slow cooker again and cook for another 15 to 20 minutes, or until the cheese is melted and bubbly.

Turn off the slow cooker and carefully remove the lid. Sprinkle the chopped fresh parsley over the finished casserole.

Allow the casserole to rest uncovered for about 10 minutes before serving. Spoon the warm casserole onto plates.