The cold has properly arrived. The kind where the windows are dark by four and the kitchen is the only room in the house you want to be in. That's the evening for this. Not a quick supper, not a midweek improvisation, but a slow afternoon project where the oven does most of the work and you do almost none.

Pork belly is a patient cut. It doesn't reward haste. What it wants is low heat and time, four hours or so, during which the fat renders quietly down through the meat, basting it from within, until the flesh is soft and yielding and the thin layer of skin on top has turned into something entirely different: crackling so brittle it shatters at the touchof a knife. The kitchen fills with a smell that is, I think, the closest cooking gets to a form of central heating. Pork fat and rosemary and something sweet from the onions underneath.

I make this through the winter months, from the first real frost until the clocks go forward. It's not a dish that makes sense in warm weather. You need the cold outside to justify the warmth of it. I wrote in the notebook once: "Pork belly. Sunday. Rain all day. Fed four. Nothing left." That's the highest compliment a roast can receive.

Get the best pork you can. A proper piece from a butcher who can tell you where it came from, with a good ratio of meat to fat and skin that's been scored properly. This is not the place for a supermarket shrink-wrap. The animal matters. The rearing matters. A recipe is a conversation, not a contract, but the conversation starts with the ingredient.