Bechamel Sauce

Pour the milk into a pan with the onion half, the bay leaf and the peppercorns.

Warm it over medium heat for 4-5 minutes, until the surface trembles and steam comes off it steadily.

Take it off the heat before it boils and leave it to infuse for 20 minutes.

Strain the milk into a jug and discard the onion, bay and peppercorns.

Keep the milk warm, or at least not fridge-cold. Warm milk goes into a roux far more easily than cold.

Melt the butter in a heavy pan over medium-low heat, until it foams without colouring.

Stir in the flour with a wooden spoon; it comes together as a smooth paste at once.

Cook the roux for 2-3 minutes, stirring the whole time, until it smells faintly of biscuits and has loosened slightly.

Keep it pale. Cooking the flour is what takes the raw taste out and no amount of simmering later removes it, but a roux taken to gold thickens noticeably less, so this one stops at blond.

Take the pan off the heat and pour in about 100ml of the warm milk.

Beat it until the paste is completely smooth before another drop goes in.

Lumps form in the first minute or not at all. Once flour has taken up milk in clumps the only remedy is a sieve, so the first two additions are the ones to be patient over.

Add the rest of the milk in four or five additions, beating each one smooth over low heat before the next.

Cook over low heat for 8-10 minutes, stirring constantly and reaching into the corners of the pan with the spoon.

Give it the full ten minutes. The starch needs the time to swell, and a sauce pulled off as soon as it thickens still tastes chalky.

Watch the base rather than the surface. Bechamel catches and scorches faster than it looks like it will, and a burnt sauce tastes burnt right through with nothing to be done.

Stop when it coats the back of the spoon and a finger drawn across leaves a clean line — the same test as the vanilla custard in this collection.

Grate in the nutmeg and season with the fine salt.

Taste and correct the salt.

Push it through a fine sieve while it is hot if lumps have got away from you. It works, and it is not a defeat.

Learn the ratio rather than the numbers: equal weights of butter and flour, with the milk setting the thickness. 50g of each with 600ml gives a pouring sauce, the same roux with 400ml gives something thick enough to hold its place in a lasagne, and with a litre it barely coats a vegetable.

Press a piece of cling film onto the surface if it is not going straight into a dish, since a skin forms within a few minutes.

Cool it in a shallow container, refrigerate within two hours and use it within three days.

Reheat it over low heat with a splash of milk, whisking, since it sets almost solid in the fridge.