Soupe aux pois cassés

• 1 lb (500 kg) split peas, soaked overnight in cold water
• 1 lettuce, chopped

Put the drained split peas, lettuce, carrots, potatoes, garlic, onion, bouquet garni, bacon and pepper into a large saucepan with 3½ pints (2 litres) cold water, bring to the boil and simmer for 1½ h