Grease the crockpot insert lightly with butter or cooking spray.
Layer half of the sliced potatoes evenly in the crockpot.
Add half of the diced ham and chopped onion over the potatoes.
Sprinkle with half of the shredded cheese.
Repeat layers with remaining potatoes, ham, onion, and cheese.
In a bowl, mix milk, heavy cream, melted butter, garlic, salt, pepper, and paprika.
Pour the mixture evenly over the layered ingredients.
Cover and cook on LOW for 4 hours until potatoes are tender.
Check seasoning and adjust if needed.
Let the casserole rest for 10 minutes before serving.