To a 4 quart or larger slow cooker, add bacon, potatoes, onion and chicken stock and stir to combine. Cover and cook on LOW for 6-8 hours, or HIGH for 3-4 hours, until potatoes are very tender.
Combine evaporated milk and cornstarch, whisking to combine until no lumps remain. The last 30 minutes of cooking, add cream cheese, cornstarch/milk mixture, shredded cheddar, salt, pepper and celery seed. Stir to combine, cover and continue cooking 30 minutes.
Remove lid and mash about half of the potatoes with a potato masher to thicken the soup up even more.
Serve garnished with any of the toppings. Leftovers can be refrigerated in an airtight container for 3-4 days.