1. Wash peas well and place in a large saucepan with bones and water.
2. Bring to the boil, skimming when necessary.
3. Add onion, cover and simmer very gently for 2 1/2 hours.
4. Remove bones and scrape off meat.
5. Rub soup through sieve. Return meat to soup. Season to taste with salt and pepper and stir in a little more water if too thick.
6. Reheat soup and serve with croutons or toast.
7. Dutch pea soup: Simmer 1 Rookwurst sausage in water for 30 minutes — do not boil.
8. Slice into soup tureen and add hot soup.
9. Cooking tip: To prevent split peas sticking to base of saucepan, do not stir during cooking.