Overshadowed by rocket, which is so tediously ubiquitous, watercress struggles to get a look-in. Curious that, because the latter is by far the superior leaf. With watercress you get that reliable, but not overbearing pepperiness, all bound up in juicy, sappy succulence. It's a two-in-one vegetable: the leaves have the velvety floppiness of lamb's lettuce, while the stalks have the snap of beansprouts. To salads, a tangle of watercress lends a blast of deepest green taste and bouncy volume. It makes sandwiches (rare roast beef, egg mayonnaise) lively and fresh. Providing you have a blender, no soup is simpler than watercress.

Why is watercress good for me?
There's a stack of good nutrition packed in this watery plant, especially if you eat it raw. It is a rich source of vitamins and minerals, but contains particularly high levels of bone-building and strengthening vitamin K, and vitamin A, which is important for eye health.

Watercress also contains significant levels of glucosinolate compounds and many studies now suggest that these have anti-cancer effects. Eating these compounds appears to help inhibit breast, lung, colon, and prostate cancers. Flavonoid antioxidants in watercress (carotene, lutein, zeaxanthin) also support good vision, have benefits for the cardiovascular system, and help protect cells against damage from free radicals.

Where to buy and what to pay
English watercress really does knock spots off the Dutch and French competition. Watercress tends to get sold in tired salad mixes, but there is some great watercress on sale in its own right – particularly the organic sort, which looks particularly green and packed with vitality. Guide price: £1.30/100g.

Joanna Blythman is the author of What To Eat (Fourth Estate, £9.99). To order a copy for £7.99 with free UK p&p, go to theguardian.com/bookshop

Watercress potatoes with smoked trout

Watercress has a wonderfully peppery flavour, which is a good foil for smoked fish. Although I generally use it raw in salads – at this time of year it's great with pink grapefruit or blood oranges and smoked fish – it is delicious cooked too. This is a quick supper dish. I sometimes leave out the smoked trout and serve the potatoes as a garnish to a piece of steamed fish.

Serves 4
800g main crop potatoes, eg king edward which has a good balance between waxy and floury, peeled and sliced into 2cm-thick slices
A small bunch of spring onions, trimmed and sliced
2 bunches of watercress, washed and large stalks removed
A splash of flavourless oil
150g creme fraiche
200ml skimmed milk
250g smoked trout, skinned, boned and flaked
1 tsp creamed horseradish (optional)
A squeeze of lemon
Salt and black pepper

1 Preheat the oven to 180C/350F/gas mark 4. Put the potatoes in a large pan of salted coldwater, bring up to the boil and simmer for 5-7 minutes until al dente - the flesh should give a little if you insert a sharp knife into the middle.

2 Meanwhile make the watercress cream. In a lidded pan large enough to take the watercress, add a generous splash of oil and heat over a medium to high heat. Add the watercress and toss until it starts to wilt. Put the lid on for a minute, so that the stalks soften.

3 Remove the lid and pour in the milk, bring to a simmer and add the creme fraiche, then pour the whole lot into a food processor and whizz to a green, flecky sauce.

4 When the potatoes are ready, drain and refresh under cold water so they don't cook any more. Toss the sauce and potatoes together, season to taste and spoon half of them into a baking dish that will fit them all snugly.

5 Mix together the smoked trout, spring onions, horseradish and lemon.

6 Flatten out the potatoes and cover with the smoked trout mixture. Cover with the rest of the potatoes, pouring over any remaining watercress sauce.

7 Place on a baking tray in the oven and bake for about 25-30 minutes until the potatoes are completely cooked.

Rosie Sykes is head chef of Fitzbillies (fitzbillies.com) and co-author of The Kitchen Revolution (Ebury Press, £25). To order a copy for £19.99 with free UK p&p, go to theguardian.com/bookshop