• 25 g/1 oz butter
• 1 medium-sized onion
• 225 g/8 oz (1 large) potato
• a scant litre/1½ pints chicken stock
• 225 g/8 oz mixed lettuce and spinach
• handful fresh mint
• salt and freshly milled pepper

Melt the butter in a saucepan. Peel and chop the onion and add to the butter. Fry gently for about 5 minutes or until the onion is soft and tender but not brown. Peel and dice the potato and add to the pan. Toss in the onion-flavoured butter and then stir in the stock. Bring up to the boil, then lower the heat and allow to simmer for about 15 minutes or until the potato is tender.

Meanwhile wash the lettuce, spinach and mint well in two or three lots of cold water. Strip away the lettuce stalks and pull away the stem and mid-rib from the spinach leaves. Strip the mint leaves from the stems. Add all the greens at once, bring back to the boil and simmer for 10 minutes. Draw the pan off the heat and pass the soup through a vegetable mill. If preferred blend the soup to a purée in a blender, in which case sieve the soup afterwards to remove the small stalky pieces that will inevitably come from the mint. Check seasoning with salt and pepper and allow to cool. Chill for several hours before serving.