A paradox in a bowl: this soup has a lovely, clean, delicate flavour, even though it's sinfully enriched with cream, and thickened with egg yolks. If you like a fresh-tasting soup, as I do, you'll love this one.
This recipe is adapted from Robert Carrier's recipe for Potage à la Bonne Femme, from Great Starters, a little gem of a book first published in 1965.
Of the nine soups Carrier included in this book, no less than three feature lettuce as the main ingredient. Having tasted this soup, I can see why: when softly stewed in butter and stock, the humble and unfashionable iceberg lettuce has an ethereal yet distinctive taste, as does cucumber, that most gentle of flavours.
Carrier's original recipe suggested chervil, sorrel or tarragon as a flavouring herb, but I used fresh parsley (I couldn't find any fresh chervil or sorrel, and I thought tarragon would overpower the dish).
This soup is a bit tricky to make, because the eggs have a tendency to curdle in the blinking of an eye. If you're not confident about adding eggs to hot soup, I suggest you add a little cornflour (see recipe) and only two egg yolks to the mixture, which will greatly minimise (but not eliminate) the chances of the soup splitting. If it does curdle, for whatever reason, strain the whole lot into a liquidiser and blitz until smooth - it will still taste lovely.
Lettuce, Cucumber, Spring Onion and Pea Soup
5 t (25 ml/25 g) butter
1 small iceberg lettuce, finely shredded
6 spring onions [scallions], white and pale-green parts only, finely sliced
250 g frozen peas
half a large cucumber, peeled, deseeded and cut into matchstick-sized pieces
salt and freshly ground pepper
6 cups (1.5 l) good chicken stock, heated
3 egg yolks (or two egg yolks, plus 1 ½ t [7.5 ml) cornflour/cornstarch]
200 ml single cream
3 T (45 ml) very finely chopped fresh parsley or chervil
Heat the butter in a large pot and add the lettuce, spring onions, frozen peas and cucumber. Season with salt and pepper, stir well and cook gently for five minutes. Add the hot chicken stock and simmer for 30 minutes, or until the vegetables are quite tender, but not mushy. Put the egg yolks and cream into a little bowl and whisk together until well combined. [Alternatively, see above, slake the cornflour with a few teaspoons of cream. Whisk in the remaining cream and two egg yolks.)
Add a soup ladle of the hot soup to the egg and cream mixture and stir well. Remove the soup pot from the heat and strain the egg and cream mixture, through a sieve, into the soup. Put the pot back on a very gentle heat and simmer, stirring constantly, until the soup thickens ever so slightly. Don't, whatever you do, allow the soup to come anywhere near boiling point, at which point it will curdle. Stir in the finely chopped parsley or chervil.
Check the seasoning and serve hot. Robert Carrier suggests croutons as a garnish, but I liked it just as it was.
Serves 4 - 6.