My sweet potatoes live in a cool cupboard, not the fridge

I buy sweet potatoes a few at a time: orange flesh, a sweet smell from the oven, and they suit almost any autumn supper. At first, out of habit, I put them in the fridge drawer next to the carrots. Then I noticed that when I baked them the middle stayed dense and hard, and the flavour was somehow flat, even though the skins looked perfect.

It turns out sweet potatoes don’t like the cold. They aren’t ordinary potatoes or carrots, and the fridge spoils them from the middle. They want somewhere cool, dark and dry: for me that’s the bottom shelf of a cupboard away from the cooker, in a basket or a paper bag rather than a tied-up plastic one where they sweat. I don’t wash them in advance; the soil comes off just before cooking.

Every few days I have a look through the basket. If one has started to wrinkle, it gets cooked first; if one has gone soft or mouldy, it goes in the bin. Usually within a couple of weeks the basket has emptied itself — baked whole, cubed into a soup, mashed alongside fishcakes.

When I buy sweet potatoes, I choose firm ones with smooth, tight skin and no soft ends, cracks or dark sunken spots. Medium ones of a similar size are easiest, because they cook in the same time. I don't buy more than we will use in a week or two.

The cool cupboard is the whole trick, but it does need to be cool, not warm. A shelf right next to the oven or above a radiator makes them sprout and go soft; a cold larder or a cupboard on an outside wall is ideal. If a sweet potato does start to sprout a little, I cut the shoots away and cook it soon. If it has gone wrinkled, soft or mouldy, it goes in the bin.

My everyday way of cooking them is the simplest: baked whole in their skins. I scrub them under the tap with a brush, dry them and prick each one a few times with a fork, so steam can escape. They go straight onto the oven shelf, with a tray below to catch the sticky juice, at 200°C, or 180°C for a fan oven, for forty-five minutes to an hour, until a knife slides into the middle without any resistance and the skin has started to wrinkle.

I split them open, add a little butter and salt, and that is supper with a green salad, or a side for chicken or fish. For children, I scoop the flesh out and mash it with a fork; it's naturally sweet, and the little ones love it.

Once cut, a raw sweet potato doesn't keep well, so I cut only what I need. Peeled or chopped raw pieces go into a bowl of cold water and get cooked the same day, because they darken in the air.

Leftover cooked sweet potato is useful the next day: mashed and spread on toast, stirred into soup, or mixed into fishcakes. I cool it, cover it and put it in the fridge within two hours, eat it within two days, and reheat it until it is steaming hot all the way through.

Sweet potatoes also roast beautifully in wedges or cubes. I toss them with a spoonful of oil and a pinch of salt, sometimes paprika, and spread them in one layer on a tray at 200°C for twenty-five to thirty minutes, turning once. Their sugars catch easily, so I keep an eye on them in the last few minutes.

Cooked sweet potato is another story: leftovers go into the fridge within an hour or two and get eaten within a couple of days. The raw ones can lie quietly in the dark and wait for their evening.