The best roasting roots come out of cold ground

There is a particular pleasure in a tray of roots that have been through a frost. Cold ground does something to a parsnip: the starches turn to sugar, and what was woody in October becomes honeyed by December. Carrots get sweeter, beetroot deepens to something almost winy. If you grow your own, or buy from a farm stall where the veg was lifted that morning, you are already halfway to a good dinner.

This is the traybake I make more than any other between November and March. It takes about ten minutes of actual work, fills the kitchen with the smell of thyme and caramelising honey, and sits happily beside roast chicken, a pie, or nothing but a bowl of buttered lentils. The trick is not in the ingredients. It is in the order you add them.

Choosing and cutting your roots

You want roughly a kilo and a half of roots for a tin that will hold them in a single layer. Crowding is the enemy: packed together, they steam and go limp rather than catching and browning at the edges.

• Carrots — scrub rather than peel if the skins are clean. Leave small ones whole with a stub of green top attached; halve or quarter anything fatter than a thumb.
• Parsnips — peel them, then quarter lengthways and cut out any woody core from the big ones. Slim parsnips can simply be halved.
• Beetroot — scrub, don't peel, and cut into wedges a similar size to everything else. Wear an apron; the juice stains.

Keep the pieces roughly even, about the size of a wine cork, so everything finishes at the same moment. If you have a few small potatoes or a red onion going soft in the basket, they belong here too.

The tray, the fat and the heat

Set the oven to 200°C fan, 220°C conventional, gas mark 7. Put your largest roasting tin in to heat with two or three tablespoons of fat — dripping, goose fat, or a good cold-pressed rapeseed oil if you want the roots' own flavour to lead. Give it five minutes, then tip in the roots. They should sizzle on contact. That immediate hiss is what builds the crust.

Toss everything in the hot fat with a generous pinch of flaky salt and plenty of black pepper. Spread out, tuck in a few whole sprigs of thyme, and roast for 35 to 40 minutes, turning once at the halfway mark with a spatula rather than a spoon so you keep the flat faces that have started to colour.

Beetroot will bleed and stain its neighbours pink. Most of us don't mind. If you do, roast the wedges in their own small tin for the first twenty minutes and add them to the main tray afterwards.

Honey, thyme and cider vinegar — the finishing move

Here is where a good traybake becomes a memorable one. Honey added at the start will burn to bitterness long before the parsnips are tender. Add it in the last ten to twelve minutes, and it glazes rather than scorches.

Drizzle over two tablespoons of runny honey — heather honey is superb here, dark and slightly bitter, though any good local honey will do. Strip the leaves from four or five sprigs of thyme and scatter them over, reserving a few for the table. Turn everything once to coat, then return to the oven until the edges are sticky and the beetroot is yielding to a knife.

Then, off the heat, comes the vinegar. Two teaspoons to two tablespoons of cider vinegar, splashed straight into the hot tin, will lift every bit of caramelised honey off the metal and turn it into a sharp, glossy dressing. Taste a wedge. If it needs more, add more. The vinegar is what stops the whole dish tipping into sweetness, and it is the step most people skip.

Growing and foraging your own thyme

Thyme is the easiest herb to keep going in a British garden. It wants sun, sharp drainage and a bit of grit in the planting hole, and it will sulk in wet clay. A pot by the back door does fine. Trim it after flowering to keep it bushy, and you will have sprigs all winter.

Wild thyme grows on chalk downland and close-cropped heath, low and creeping, and you will smell it before you see it. If you forage, pick only a few sprigs from any one plant, take nothing from nature reserves, and get the landowner's permission on private ground. Never uproot. Marjoram, winter savory and wild fennel all behave in much the same way in this recipe.

Leftovers and the scrapings of the tin

Cold roast roots are excellent. Fold them into a grain salad with plenty of parsley, or chop them small and fry with an onion for a bubble-and-squeak style cake. The sticky residue in the tin, loosened with a little hot stock or water while it is still warm, makes a fine instant sauce for a roast.

Cook it once and it will become a weekly habit until the ground thaws. That, more than any technique, is what seasonal cooking looks like: a tin of roots, a spoon of honey from a neighbour, thyme from a pot, and vinegar sharp enough to keep it all honest.