Sauté veggies: In a large stockpot or Dutch oven over medium-high heat, saute the onion, carrot, celery, and garlic in butter. Stir only occasionally to prevent burning. Allow to cook for about 10 minutes.
Combine ingredients: Add rinsed soaked beans to the pot. Use a sharp knife to make cuts in the ham hock and place it in the pot. Add the liquid (chicken broth, water, vegetable broth - whatever combination you choose), oregano, nutmeg, and bay leaves. Do not add the apple cider vinegar.
Simmer: Bring soup to a boil over high heat. Reduce heat to maintain a simmer. Do not cover. As the soup cooks and the liquid evaporates, heat may need to be reduced to maintain a gentle simmer. After about an hour of cooking, remove the ham hock and transfer it to a cutting board (look ahead to next step). Cook until beans are tender, about 90 minutes to two hours. It may take less time depending on how soft the beans got after your soak.
Cut ham: As soon as the ham hock is cool enough to handle, cut any meat into small pieces and return to soup. Discard any skin, fat, and bones.
Add the secret ingredient: When the beans are completely soft and the soup is ready to eat, stir in the apple cider vinegar. Taste, and add salt and pepper, as desired. To thicken, you can process about 2 cups of the soup in the blender and mix it back in.
To serve: Remove bay leaves and enjoy with cornbread.