Grease the slow cooker by generously spraying/coating the sides in your preferred oil.
Layer the potatoes and ham into the pot (I usually start with potatoes on the bottom). Do this until all are used.
In a small measuring cup, stir together the butter, onion powder, pepper, thyme, rosemary, and mustard. Whisk until no lumps remain.
Pour the butter mixture over the potatoes and ham in the slow cooker.
Cover the pot and cook on high for 4 hours or low for 6 hours.
Optional step: You may stir in the sour cream or yogurt for an extra creamy dish.
Remove the lid and sprinkle the cheese over the top.
Scoop out your servings, cover with more cheese or sour cream as you like, and enjoy!