Lettuce and Mint Soup

• 50 g (2 oz) butter
• 1 onion, peeled and diced

Melt the butter in a heavy saucepan. When it foams, add the onion and potato, and turn them until well coated. Sprinkle with salt and pepper. Cover, and sweat on a gentle heat for 10 minutes. Add the chopped lettuce leaves and stock. Boil until just tender, but do not overcook or the lettuce will lose its colour and flavour. Make a purée in a blender or food processor, after cooling slightly fi