Rinse your pre-soaked beans thoroughly under cold water, removing any debris or misshapen beans.
Place your ham hock or diced ham at the bottom of your slow cooker.
Add the rinsed beans on top, followed by the diced onion, garlic, carrots, and celery.
Sprinkle in the dried thyme, black pepper, optional cayenne pepper, and tuck in the bay leaf.
Pour in your chicken broth or water until the beans are covered by about 2 inches of liquid. Add the apple cider vinegar.
Cover your slow cooker and set to low for 6-8 hours or high for 3-4 hours.
About 30 minutes before serving, remove the ham hock (if using), shred the meat, and return it to the pot.
Taste and adjust seasonings, adding salt only at this point as needed.
If you prefer a thicker consistency, mash about 1 cup of beans against the side of the pot and stir back into the mixture.