Place all ingredients in the Crock-pot, cover and cook on HIGH for 4 hours. Remove the onion with a slotted spoon and discard. Carefully remove the ham bone and any smaller pieces of bone. Use an immersion blender (or transfer to a blender in batches) and pulse the soup several times to thicken it. You can puree until smooth, as I did, or leave bite size chunks in the soup. Leave the pureed soup uncovered and cook on HIGH for another 2 hours, stirring occasionally. Cook until it has thickened. Enjoy!