Winter produce in Punjab: saag, gajar, muli and what to do with them.

Why do cold nights sweeten winter sabzi?

It is not sentiment, it is the plant protecting itself. When night temperatures drop towards freezing, root crops and leafy greens convert some of their stored starch into sugars, because sugar dissolved in the cell sap lowers its freezing point. The plant is making its own antifreeze, and the side effect is that it tastes sweeter to us.

This is why a gajar pulled in December is a different vegetable from one pulled in October, and why saag made from the first thin bundles of sarson in November is sharper than the same saag in January. It is also why the season has an end you can taste: once the nights warm up in late February the greens shoot upward, put out flowers and turn bitter and stringy almost overnight.

Saag: the mix matters more than the recipe

Sarson on its own makes a harsh saag. Mustard greens carry the same pungent compounds as mustard seed, so a pot of pure sarson comes out sharp and slightly bitter, and it stays thin. Nobody in a Punjabi kitchen actually cooks it that way. The working proportion is roughly three parts sarson to one part palak, plus a good handful of bathua and a small handful of methi if you want an edge to it.

Each green is doing a job. Palak takes the bite off and gives the pot its body, because spinach breaks down into a soft pulp. Bathua adds a mineral depth and helps the texture. Methi is the seasoning green — a little makes the whole pot taste more like itself, and too much makes it bitter. Buy them as separate bundles and mix them yourself; the pre-mixed chopped saag sold ready to cook is convenient but you cannot see what went into it.

Cook it slowly with green chilli, plenty of adrak and lehsan and just enough water, then mash it with a wooden mathni worked in the pot, which crushes the leaves without turning them to the smooth purée a blender gives — texture is half the point of saag. Thicken with two or three spoons of makai atta whisked into cold water first so it does not lump. Finish with a tarka of sliced onion, garlic and whole red chilli.

• Roughly three parts sarson to one part palak, plus bathua, plus a little methi.
• Wash in a big tub, lift the leaves out of the water rather than pouring, and repeat until no sand settles.
• Mash rather than blend, so the saag keeps some texture, and cook it a day ahead — it is better on the second day.
• Makki di roti is the classic partner, but a hot whole-wheat roti with a knob of makhan does the job just as well.

Gajar: desi red or hybrid orange?

Two different carrots share one name in winter and they are not interchangeable. The long red desi gajar is softer, juicier and less crunchy, with a thinner core, and it is the one halwa wants: it grates into soft threads, it releases its water into the milk and it gives the halwa its colour without any help. Orange hybrid carrots are crisper, hold their shape and stay sweet raw, which makes them right for salad, pulao and anything cut into batons.

Buy gajar with the leafy tops still attached where you can, because perky green tops mean it was pulled recently and limp yellow ones mean it was not. Then twist the tops off before you store it: leaves left on keep pulling water out of the root and a bunch of carrots goes limp in the fridge within days. Both kinds should snap crisply rather than bend.

Beyond halwa, red gajar is what kanji is made from — batons left in water with ground rai, kala namak and red chilli, jarred and stood in the winter sun for several days until it turns tart and fizzy. Black carrots make it darker still where you find them.

Muli and shalgam: buy small, twist off the leaves

The single rule with muli is to buy small to medium. A giant white radish looks impressive and is almost always pithy — hollow, dry and spongy at the centre — and it will be aggressively hot as well. A small firm muli, heavy for its size with taut skin, is mild enough to eat raw in slices with salt. Snap the tip: it should break, not bend.

Do not throw the greens away. Muli ke patte are cooked exactly like any other saag, chopped down and cooked slowly with onion, garlic and chilli, and they have a pleasant peppery bite. They wilt faster than the root does, so cook them within a day or two. Grated muli squeezed dry and stuffed into paranthe is the other classic use, and squeezing it properly is the difference between a parantha and a wet mess.

Shalgam follows the same rule for the same reason: small and firm, with smooth unblemished skin and no give. Large turnips turn woody at the core and taste strongly of sulphur. Shalgam gosht is the standard winter treatment, where the turnip breaks down into the salan and takes the fat with it, and shalgam is also good simply braised with gur until it caramelises.

Matar, gobhi and the rest of the winter crate

Winter matar is the best thing in the shop for about six weeks and it deteriorates faster than almost anything else, because peas start converting sugar to starch as soon as they are picked. Pods should be plump but not stretched tight, and they should feel slightly velvety. Shell them the same day. If you have more than you can use, blanch them for two minutes, drop them into cold water, drain them dry and freeze them spread on a tray before bagging, so they stay loose instead of setting into one block.

Gobhi is at its tightest and heaviest in winter — look for a dense white curd with no black speckling and green jacket leaves still clinging. Hara pyaz arrives with roots on and belongs in everything from an omelette to a keema.

One habit worth keeping: the season ends abruptly. Saag freezes well in portions, blanched matar even better, and gajar halwa freezes better than anyone expects. February is the month to cook more than you need.