Like soft round lettuces, fiery yellow mustard and corned beef, watercress is the unfortunate victim of the assumption – now, happily, being challenged on all fronts – that foreign equals better. Once upon a time the leaves, brought up in great wicker baskets from farms in the south of England, were the breakfast of choice for the working classes, either in sandwiches or, for the really poor, on their own.
Henry Mayhew notes in his 1851 survey London Labour and the London Poor: "The first coster cry heard of a morning in the London streets is of 'Fresh wo-orter-creases'. Those that sell them have to be on their rounds in time for the mechanic's breakfast, or the day's gains are lost." Eliza James, the watercress queen of Covent Garden for half a century, made her fortune with the crop, arriving at the market every day on a watercress cart, despite her great wealth.
How things have changed. My local branch of Sainsbury's offers three or four varieties of rocket, but I had to hunt hard to find a single tiny bag of "baby watercress" which proved to have about as much pungency as dijon mustard (indeed, the plant's heat comes from its mustard oils). For this recipe, you want the real stuff: big, emerald bunches, crunchy and properly peppery. Use any left over in sandwiches: with a bit of salted butter, it knocks rocket into a beret.
They may taste robust, but watercress leaves are surprisingly delicate, and long cooking of the kind recommended by Delia Smith and Jane Grigson (35 minutes apiece!) seems to rob them of flavour. Even Lindsey Bareham's quarter of an hour seems a crime.
Raymond Blanc goes for four minutes, Rowley Leigh a mere two, but swiftest of all is Denis Cotter in his book Wild Garlic, Gooseberries and Me, blanching them separately then plunging them under a cold tap to cool down before adding to the soup. Blanc adds ice cubes to his pan for the same reason: rapid cooling will help the cress to retain its flavour and vibrant colour. Blanching them separately seems the best idea here – Cotter's soup is gloriously green.
Potatoes are a popular ingredient in many soups, acting as a thickener; only Blanc and Grigson eschew them. While I love spuds, I think the pair are right here – they have a surprisingly assertive flavour, a kind of lingering starchiness that seems at odds with the fresh, green character of the watercress. Welcome in cold weather, less so here.
Grigson uses flour instead, in keeping with the teachings of the great Larousse Gastronomique, which starts all its cream soups with a white roux. I think this works very well: the flavour of the flour is far subtler than that of the potato, but it gives the soup a similarly satisfying texture.
Almost everyone starts their soup by frying onions in butter – except Smith, who uses leeks, and Leigh, who rejects all things alliaceous in his commendably simple recipe. Leeks seem misguided: like the potato, they bring a whiff of winter with them, and together the two hint strongly at vichyssoise. A fine soup, but one that doesn't require any improving with watercress.
Onion, however, to my slight surprise, is a must – it's such a strong flavour that I had assumed it would be too dominant. In fact, if cooked until soft, it brings a lovely sweetness which works very well with the peppery cress. Garlic, as used by Blanc and Cotter, seems a little too harsh.
Clearly the second most important element to a soup, and there's a variety of options on offer in the recipes I try. Blanc uses water; Leigh the potato cooking water (both thrifty and clever, if you're after a rich potato flavour); Smith, Cotter and Bareham vegetable stock and Grigson "light veal stock or water". I give chicken a try instead, having had success with it in vegetable soups in the past.
As so often, I find vegetable stock (Marigold bouillon powder, as Smith recommends) brings with it an overassertive flavour of dried herbs. Chicken blends in much better, but actually watercress is so punchy that plain old water is quite sufficient.
Most of the recipes I try are for cream of watercress soup: the peppery flavour marries peculiarly well with dairy. Leigh is the honourable exception. It's double cream for Cotter and Bareham (though she uses far more milk than cream), single or whipping for Grigson and fancy creme fraiche for Smith and Blanc, which I think adds a jarring tanginess to the finished dish.
I find Grigson's soup rather too rich for my liking, probably as much because of the egg yolks she stirs in as the cream itself. It would be a delight served in tiny cups as a starter, but a bowl would be a daunting prospect.
I miss the creamy element in Leigh's soup, though: while intensely cress-flavoured, it feels rather spartan (hence, perhaps, the poached eggs and buttered croutons he serves in it). Bareham's milk and double cream combination seems to work best, providing a certain comforting richness without overwhelming the cress.
There isn't much in the way of outlandish extras this week. Blanc adds spinach to "round up the strong peppery qualities of the watercress", which, though delicious, serves to mute the star attraction. Cotter adds a slug of white wine and a sprig of thyme, which gives it a curiously Frenchified flavour. It is, however, excellent with a glass of cold white wine – English, like the watercress, naturally.
1 onion, finely chopped
Pinch of salt
400ml whole milk
3½ bunches (about 420g) watercress, washed and roughly chopped
75ml double cream
Heat the butter in a large pan over a medium-low heat and add the onion. Season and cook gently until soft, but not coloured. Stir in the flour and cook for a minute.
Gradually stir in the milk and 250ml water. Bring to just below the boil, cover and simmer for 5 minutes.
Meanwhile, prepare a large bowl of iced water. Bring a large pan of water to the boil and plunge in the watercress to wilt, reserving a few leaves to garnish. Tip out into a colander, and then into the iced water.
Squeeze the cooled watercress out and add to the pan. Puree the whole lot thoroughly, add the cream and season to taste. Reheat if necessary: delicious hot or chilled.
Watercress: why do you love it, and what else do you like to make with it? And are there any other neglected British delicacies we should be eating more of?