Load the crock pot. Add the half and half, cream of onion soup, cheeses, celery seed, garlic, and pepper to the crock pot and mix. Then fold in the potatoes and ham until every slice of potato is covered in the cream mixture.
Cook on high for 4 hours or on low for 8 hours in the slow cooker. I recommend piercing a potato slice with a fork before turning off your crockpot, just to make sure the potatoes are cooked throughout and soft.