Drain and rinse the soaked beans, then place them in a large slow cooker.
1 pound dried great northern beans,
Add the diced ham, onion, carrots, and celery to the crockpot with the beans.
2 cups cooked ham, 1 large onion, 2 carrots, 2 celery stalks
Pour the chicken broth over the ingredients, making sure all the beans and vegetables are submerged.
8 cups chicken broth
Add the mustard, garlic powder, sage, and bay leaf and stir everything together gently to combine. Place the ham bone in the center of the ingredients, if using.
3 Tablespoons Dijon mustard, 1 teaspoon garlic powder, 1 teaspoon rubbed sage, 1 bay leaf, 1 ham bone
Cover the crockpot and cook on low for 8-10 hours, or on high for 4-5 hours, until the beans are tender and the flavors are well blended.
Remove the ham bone and cut off any excess meat. Set the bone aside and add the excess ham back into the slow cooker. Taste the soup, adjusting the salt and pepper if needed.
Salt and pepper
Ladle the soup into bowls and sprinkle with the optional fresh parsley before serving. Best when served warm.
Chopped fresh parsley