• It pays to prepare as much as possible in advance - that way every element is quick to get on with.

  Trim the meat, slice the mushrooms, clean and cut the celeriac and measure out the various ingredients.

  Doing the prep first can make a dish with several elements much easier to manage.

Celeriac purée

• Pour the milk, cream, thyme, nutmeg, peppercorns and the piece of Parmesan into a saucepan. Heat it through well, then turn down to a low heat so it is only just simmering. Leave it to infuse for the next hour or so, stirring now and then.
• Meanwhile, prepare the celeriac. Clean or peel the celeriac.

  The skin holds plenty of flavour, so you can simply scrub it well and cut off only the base, where a lot of soil hides. Alternatively, the whole celeriac can be peeled – it's up to you.
• Cut the celeriac into small dice.
• Melt the butter in a wide, deep frying pan and brown the celeriac over a fairly high heat for about 20-25 minutes. Stir regularly and continue until all the pieces are golden and nicely tender. On my hob, the setting is 7 out of 9.

  *While the celeriac is cooking, start on the tenderloin - it needs about 50 minutes in total - including browning. Then make the sauce and the mushrooms.
• Crumple a piece of baking paper and lay it snugly over the layer of celeriac, turn down to a low heat and let it continue cooking for a further 10-15 minutes. The pieces should be completely tender.
• Strain the milk mixture through a fine-mesh sieve and pour it into a blender together with the golden, tender dice of celeriac.
• Blend everything thoroughly at high speed for about 5 minutes, or until you have a smooth, even and creamy purée. Season with salt and blend it well into the purée. Keep the purée warm until the meat is ready.

Pork tenderloin

• Trim the meat of sinew and silver skin and season with salt and freshly ground pepper.
• Melt the butter in a frying pan with the oil and let it foam up well. Add the garlic and thyme and lay the tenderloins in the pan. Brown them well over a high heat – on all sides. It shouldn't take much more than 5 minutes in total.
• Place the tenderloins in an ovenproof dish, pour the contents of the pan over them and insert a meat thermometer into the thickest part of the meat.

  Finish the tenderloins in a preheated fan oven at 100°C for about 45 minutes – or until they reach a core temperature of about 60-62°C. At this point the pork will be a lovely pink.

  If you prefer the meat more well done, you can let it roast to 64-65°C.

  Let the meat rest for about 10 minutes and slice it when the dish is ready to serve.

Sauce

• Melt the butter in a saucepan and sweat the shallot in it until translucent – season with plenty of freshly ground pepper.
• Pour in the red wine and let it reduce by half over a fairly high heat. Add the stock and let it reduce by half again, then strain it through a fine-mesh sieve.
• Return the sauce to the hob over a medium heat and thicken it with a little cornflour mixed with a little cold water. Add only a little at a time – the sauce should be glossy, like a glaze – not thick.

  Then leave it over a low heat until it is to be served, and adjust the seasoning with more salt, pepper or a little sugar if you feel it lacks sweetness.

Fried mushrooms

• Melt the butter in a frying pan and fry the mushrooms over a fairly high heat until they are browned and have released their liquid. Season with salt and freshly ground pepper.

Serving

• Spoon a generous dollop of celeriac purée onto a flat plate and spread it out in a circle. Top with the pork tenderloin, fried mushrooms and a little sauce.

  Sprinkle with parsley and freshly ground pepper and serve.