Prepare the crock of a 5 - 6 quart slow cooker by generously spraying the sides.
Layer the potatoes and ham into the pot.
In a small measuring cup, stir together the butter, onion powder, pepper, thyme, rosemary, and mustard. Stir until no lumps remain.
Pour the butter mixture over the potato and ham mixture.
Cover and cook on high for 4 hours or low for 6 hours.
Remove the lid and sprinkle the cheese over the top.
Optional step: You may stir in the sour cream or yogurt for an extra creamy dish.