Soak the haricot beans overnight in water. The next day drain and rinse them well.
Place the ham in a large casserole pot, cover with water and bring to a simmer, then cook for 10 minutes before draining and discarding the water. Return the ham to the casserole along with the onions, garlic, haricot beans, bay leaf, thyme, pepper and Dijon mustard. Just cover with water, gently bring up to the boil, skim off any residue and simmer for 1½ hours with the lid on.
After the hour and a half has elapsed, add the carrots, potatoes and leeks to the casserole, cover and simmer for another 15 minutes.
Check the seasoning – you may not need to add salt. Add the green beans and parsley and cook for a further 5 minutes.
Lift out the ham, allow all the stock to run back into the casserole, and place the ham on a large carving board or plate. Slice the ham and serve it with the vegetables and cooking stock.