Place half the sliced potatoes in the bottom of the slow cooker. Add half the diced ham and half the sliced onion on top.
Repeat the layers with the remaining potatoes, ham, and onion.
In a mixing bowl, whisk together the milk, heavy cream, flour, garlic powder, salt, and black pepper until smooth.
Pour the milk mixture evenly over the layered ingredients in the slow cooker.
Sprinkle the shredded cheddar cheese across the top.
Cover and cook on low for 6 to 7 hours until the potatoes are tender when pierced with a fork.