Slice leeks, carrots and turnip and add to pot. Cut potatoes into small pieces and add to pot. Add ham shank.
Add water to cover all ingredients. Bring to the boil, then lower heat and simmer for 1 hour 30 minutes. Add boiling water if it becomes too thick. Stir occasionally to ensure it does not stick to bottom of pot. Add 1/2 tablespoon salt, or to taste, while cooking.
5 minutes before soup is ready remove ham shank. Serve soup with morning rolls or plain bread.