I LOVE root vegetables - all of them. But the celeriac root is, in my opinion, one of the most underrated, with its rough, knobbly and gnarly exterior which hides the most delicious flesh inside.

Celeriac got a lot of good press when everyone seemed to be on the carbsphobic Atkins diet because as well as containing Vitamin C and potassium, it is also very low in carbohydrates. Crispy and crunchy when raw and silky smooth when cooked, this unlikely-looking vegetable, which tastes of celery (it is a form of celery itself ) and parsley, is in season now for the rest of the winter and is hugely versatile.

In France, celeriac is often turned into celeri remoulade, a wonderful salad which is almost a national dish, where matchsticks of raw celeriac are mixed with a homemade mayonnaise, dijon mustard and lemon juice. Celeriac is also really good raw, grated or finely sliced in winter salads, but do toss it in a little lemon juice as it browns quite quickly.

A creamy celeriac soup with roasted hazelnuts is a perfect winter lunch or supper and always brings back good memories as it was the starter at our wedding eight years ago. I love mashed celeriac, which is first boiled in water then hand-mashed or puréed in a food processor with a little butter, cream and garlic or nutmeg - sometimes I add mashed potatoes to it too, or even cooked mashed chestnuts or apple purée, which is really good with celeriac.

To sauté celeriac, just cut it into small cubes and toss in olive oil on the heat until softened, or throw it into a hot oven for about 15 minutes - this is excellent with roast meat.

I Celeriac facts »Approximately quarter of the weight will be discarded during preparation (once the thick skin is removed), so keep this in mind when following a recipe.

»When preparing celeriac, it is a good idea to keep it in water with an added dash of lemon juice or white wine vinegar, which will prevent it from discolouring.

»Try to find celeriac with as smooth a skin as possible so you don't waste any flesh when peeling it. It should feel heavy and there should be no cracks in the skin. The top is the part that starts to soften first, so look at this and press it with your finger, then turn it over and give it a good prodding as the underbelly softens next » You don't have to use celeriac all in one go. Cut some off, wrap it in clingfilm and put it back in the fridge. Uncut it will last for up to two weeks; cut it will last for three to four days.

» Puréed celeriac is rich and creamy. Peel the celeriac and cut it into 2cm cubes. Keep these cubes in water with lemon juice as you go. Bring a pan of just enough salted water to the boil. Add the celeriac, reduce the heat and simmer, lid on, for about 1520 minutes, until soft - they will break up during cooking if boiled too fast.

Drain well. Whizz in a food processor, adding butter and single cream until you get the texture you want.

Taste and season before serving. Try with: pork chops.

» To roast celeriac:

preheat oven to 190ºC/gas mark 5. Put a roasting tin with 1cm of vegetable oil into the oven to heat. Peel the celeriac and cut it into chunks the size you can handle. Keep these chunks in water with lemon juice as you go. Bring a pan of just enough salted water to the boil. Add the celeriac, reduce the heat and simmer, lid on, for four minutes. Drain well.

Remove the tin from the oven and coat the celeriac in the oil. Season well, then roast in the top of the oven until the celeriac is brownand soft, about 40 minutes. Remember to turn occasionally.

Alternatively, you can roast them beside your joint. Try with: any roast meats.

Celeriac soup with roasted hazelnuts Serves 4-6 This is such a good soup that will freeze well too.

25g butter One medium onion, peeled and chopped One medium potato, peeled and chopped One small to medium celeriac, peeled and chopped Salt and pepper Approx 900ml chicken or vegetable stock 75ml cream To serve:

A handful of roasted and roughly chopped hazelnuts In a saucepan, melt the butter, then add the chopped onion, potato and celeriac. Season with salt and pepper, then cover with a butter wrapper or greaseproof paper, and a lid, and cook over a low heat, stirring regularly, for about seven or eight minutes.

Add the stock, bring it up to the boil, and simmer for another 10 minutes until the vegetables are all soft. Add the cream and the chopped herbs and liquidise the soup until it is smooth and velvety. Taste for seasoning. To serve, ladel into warm bowls and sprinkle with chopped roasted hazelnuts.

Gratin of potato and celeriac Serves 4-6 This is a delicious vegetable gratin that we make at the cookery school.

900g potatoes, peeled and thinly sliced One medium celeriac, peeled and thinly sliced 300ml cream One tsp chopped tarragon or marjoram Salt and pepper Preheat the oven to 190ºC, gas 5. Peel the celeriac, cut into quarters, and slice thinly. Put the slices into a bowl of water with a dash of vinegar or lemon juice to prevent it discolouring.

Blanch both the potatoes and the celeriac for just 30 seconds in boiling water, then drain and refresh in cold water. Drain the slices and dry them.

In a gratin dish, arrange alternate layers of potato and celeriac, ending with a layer of potato. Season each layer with salt and black pepper. Add the chopped herbs and pour over the cream. Bake the gratin for about an hour until cooked through and golden and bubbly.

Roast chicken with apple celeriac and hazelnut stuffing Serves 4-6 This is a wonderful wintery recipe from Sophie Grigson's book, Vegetables, published by Collins.

One plump and happy freerange chicken A little olive oil Half a celeriac, peeled and cut into 'chips' Salt and pepper For the stuffing:

Half a celeriac, peeled and finely diced One onion, chopped Two cloves of garlic, chopped 30g butter Eight sage leaves, chopped One eating apple, cored and diced small 40g roasted, skinned hazelnuts (the skins come off while they roast, just rub them and the skins will fly away), chopped 80g soft white breadcrumbs One egg, lightly beaten Preheat the oven to 200ºC, gas 6. To make the stuffing, begin by sautéing the celeriac, onion and garlic together in the butter until tender - take plenty of time over this, say 10 minutes or more, so that their flavours really get a chance to develop. Stir in the sage leaves and cook for a further 30 seconds or so.

Now mix the vegetables and buttery juices with the apples, hazelnuts, breadcrumbs, seasoning (be generous with it) and enough beaten egg to bind.

Fill the cavity of the chicken with the stuffing.

Place the stuffed bird in a roasting tin and smear a little olive oil over its skin.

Season generously with salt and pepper. Pour a small glass of water around the bird and surround with the celeriac chips.

Roast for about 1 1/4 to 11/2 hours, depending on the size of the bird, basting the bird occasionally with it's own juices (add a little more water if it needs it) and turning the celeriac chips occasionally - they should soften and catch a little brown here and there.

Test to make sure that the chicken is cooked when the leg feels loose in the carcass and the juices from the thigh run clear. When it is cooked allow it to rest for about 20 minutes before carving and serving.

BOOK OF THE WEEK The brandnew Vegetables by Sophie Grigson, published by Collins, is full of great recipes and advice on how to buy, prepare and cook both familiar and more unusual vegetables. From artichokes to zucchinis, this book covers them all.