Melt butter or bacon fat in a pan. Add carrots. celery and onions and cook and stir until onions are soft. Add the peas and cook for a few minutes with lid on pan, stirring occasionally. Add stock and ham shank or knuckle. Cover and simmer until the peas are tender.
Remove ham or knuckle end and blend the soup using a handheld liquidiser or in a food processor until smooth. Transfer back to the pan and add pepper and chopped mint or parsley. If preferred add small pieces of chopped ham from the shank back into the soup. Ladle into warmed bowls and serve hot.