I have just been to a cookery festival called Madrid Fusión, where chefs from all over the world gathered to demonstrate favourite recipes and techniques. Present were all the stars of the culinary world, and debate on the future of food and the nature of “molecular gastronomy” raged among the likes of Ferra Adrià, Heston Blumenthal, Andoni Aduriz and Harold McGee, the brilliant writer who first made molecular gastronomy accessible with his book On Food and Cooking.

It was a fascinating display of cooking from a country that for many years was known for its delicious but relatively simple cuisine. Every chef seemed fiercely driven to produce maximum pleasure and emotion in the eater. Most of the emphasis was on simple, seasonal ingredients and how to highlight their natural flavour. Vegetables and meat were steamed, poached, sautéed; their skins were dried, frozen or fried; their cooking-water juices were made into foams, jellies, milks, purées and even scents.

One of the vegetables chosen was the humble celeriac, a root vegetable in season now. Celeriac is just as good raw as it is cooked. One of its classic pairings is with Bayonne ham, but slices of leftover ham from a roast will do you proudly. Finely slice and then julienne the celeriac and toss it in a mustardy, light mayonnaise for a light and delicious lunch. I also love it sliced wafer thin in a salad with blue cheese and toasted walnuts. Remember when eating it raw to keep it in acidulated water the second you slice it to keep the pieces pearly white (they discolour very easily). For more filling options, slice layers for a delicious gratin; substitute celeriac for half the potatoes to make a delicious mash; or roast it in the oven with garlic - it goes well with venison, duck and beef.

Or try this silky celeriac soup, inspired by a simple potato soup that I tried on my first trip to Spain many years ago. Soft pieces of potato and celeriac are suspended in a thick purée flavoured with extra virgin olive oil, garlic and fennel seeds. Fennel grows everywhere, so if you see it sprouting in the summer take some home with you. The two ingredients bring out the best in each other. This soup is good enough for a starter for a smart dinner party and is not too expensive.

Celeriac soup

Cooking time: 35 min

Preparation time: 20 min

Ingredients

1 celeriac

5 floury potatoes

120ml extra virgin olive oil

1 large onion, very finely chopped

1 tsp fennel seeds, ground

10 cloves garlic

Juice of half a lemon

1.5 litres light chicken or vegetable stock (if you are using a stock cube, don't use more than half)

Sea salt and freshly ground white (or black) pepper

Method

1 Peel and then dice the celeriac and potatoes into 2cm pieces and drop them into a bowl of water; add a good squeeze of lemon or a dash of vinegar to keep the vegetables a pure white colour.

2 Heat a large casserole pan over a medium-low heat and add all but two tablespoons of the oil. If you heat the oil too much you will lose all its flavour, so the aim here is gentle cooking. Add the onion and fennel seeds and cook over a low heat until the onion is translucent and melting into the oil, about ten minutes.

3 Meanwhile, bash the garlic cloves to loosen the skin, peel and remove any inner green stems, which have a nasty bitter flavour. Finely chop and add to the pan, cooking for another few minutes. Add the drained celeriac and potatoes. Season well with salt and pepper and cook for another five minutes, turning the vegetables to coat in oil.

4 Cover with the hot stock and simmer for about 20 minutes until a knife pierces the vegetable pieces easily.

5 Add the lemon juice and use a stick blender to blend the soup for only a minute or two. The aim is to have a thick, silky soup texture, but with half the chunks of potatoes and celeriac still intact. Serve with the remaining olive oil drizzled on top and a good grinding of black or white pepper.

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