January is meant to be a time for restriction rather than indulgence – but I can't begin to think about denial when it is freezing. If I couldn't comfort-eat, life would seem all the more miserable. I've decided to go completely the other way and give you the richest, most delicious gratin of potatoes ever. Known as dauphinoise, it is laced with nutmeg, garlic and cream, finished with Gruyère and cooked in the oven until it is golden.

No meat works with dauphinoise quite as well as beef; here I have given you recipes for the simplest dinner, and at this time of year perhaps also the most delicious.

As this dinner is so simple, the quality of the ingredients is vital. Ask your butcher for a fillet of beef that is free range and grass-fed; it should be aged for at least 28 days.

Skye Gyngell is head chef at Petersham Nurseries, Church Lane, Richmond, Surrey, tel: 020 8605 3627, petershamnurseries.com

Fillet of beef

This is a really good way of cooking beef. Although the cooking time sounds very brief, the resting time is what is important – this will give you beef that is pink but not rare.

Serves 6

1kg/2lb beef fillet, trimmed
Sea salt and black pepper
1 tbsp olive oil

Heat the oven to 240C/450F/Gas8. Season the beef really well with salt – I do mean generously, for the salt will give the beef a lovely crust. Season with pepper.

Place a pan large enough to hold the beef over a high heat on top of the stove. Once the pan is really hot, pour in the oil – it should sizzle. Now lay the beef in the pan and cook without turning for three to four minutes, then turn and brown the underside for a further four minutes. Transfer to a roasting tray and place on the middle shelf of the oven for 15 minutes, then remove. Once the beef is cool enough to handle, remove from the tin and wrap in plenty of aluminium foil, three to four layers thick. Place in a warm spot – just above the oven is perfect. Leave to sit for half an hour, before slicing and serving. Cut into generous one-inch slices and serve with the dauphinoise (recipe below).

For the gravy

1 tbsp Dijon mustard
375ml/13fl oz full-bodied red wine
Salt and pepper

I don't like meat that is covered with thick sauces; I find them too heavy. I think it's hard to cook out the flavour of the flour used for thickening – it's too cloying altogether. To make this delicious, thin gravy, once the beef has been removed from the pan, pour off the fat into a dish and place over a medium heat on top of the stove. Add the mustard and stir well, to gather all the juices from the base. Pour over the wine and stir again, then simply let the wine reduce by a third. Taste for seasoning and serve in a jug alongside the beef.

Dauphinoise potatoes

The best potatoes to use in gratins are desiree. Waxy rather than floury, they keep their shape and absorb the flavours with which they are cooked.

Serves 6

11/2kg/3lb desiree potatoes, peeled and cut into slices that are eighth of an inch thick
900ml/11/2 pints whole milk
750ml/11/4 pints double cream
Plenty of freshly grated nutmeg
3 cloves of garlic, peeled and finely chopped
Salt and pepper
150g/5oz grated Gruyère

Put the sliced potatoes in a large saucepan and pour over the milk. Season with a good pinch of salt and place over a medium heat. Once the milk has begun to simmer, immediately turn down the heat to low and cook for 15 minutes. The potatoes should just be starting to become tender. Drain and discard the milk.

Heat the oven to 180C/350F/Gas4. Place the warm potatoes in an ovenproof bowl large enough to hold all the ingredients and pour over the cream. Grate in the nutmeg, add the garlic and season with salt and pepper. Scatter over the Gruyère. Bake on the middle shelf of the oven for 40 minutes, or until the top is golden-brown and the cream oozing out over the sides. The potatoes should also be tender when pierced in the centre with a small, sharp knife. Serve alongside the beef with nothing more than a simple green salad.