Spices in Bangladeshi cooking

The two spices that go into the oil first across most of South India, and the order matters: mustard pops, then turmeric goes in off the heat. Turmeric burns in seconds at the temperature mustard needs, and burnt turmeric is bitter in a way no amount of later seasoning fixes.

How: Mustard until it crackles, then turmeric with the pan off the heat

Add alongside: Cumin, Fenugreek, Coriander leaf

• Turmeric goes in after the mustard has popped, not with it.

Mustard and brassicas are family — broccoli and mustard seed are both Brassicaceae — and the pairing works on the same sulphur chemistry from both sides. Popped in oil the mustard is nutty rather than pungent, which lifts the vegetable instead of doubling its bitterness.

Add alongside: Turmeric, Garlic, Lemon

Both are sweet-citric seeds and they reinforce rather than contrast, which is the useful thing to know: this is a pair for building a rounded base, not for adding tension. It appears together in panch phoron, in Bengali and Gujarati spicing, and in fennel-forward sausage seasoning.

Add alongside: Cumin, Mustard seed, Fenugreek

Aloo with kalonji is a Bengali staple, and it is one of the clearest demonstrations of what the seed is for. Potato is bland and absorbent, nigella is peppery and herbal and stays intact, so every few mouthfuls carry a small burst of flavour against a neutral background. Ground into the dish it would disappear; left whole and bloomed in fat first, it defines it.

How: Bloomed in hot oil at the start of a dry potato sabzi; With panch phoron in a mixed vegetable dish

Add alongside: Fenugreek, Mustard seed, Fennel seed

• Add it to hot fat rather than to the pan with the potatoes — untoasted nigella is muted and slightly raw.

Aubergine takes up a great deal of fat, and nigella is a spice that needs fat to open up, so the two arrive at the table having done each other a favour. The seed's slight bitterness also cuts the richness that makes fried aubergine heavy.

How: In the oil before the aubergine goes in; Scattered over a roasted aubergine with yoghurt

Add alongside: Cumin, Turmeric, Yoghurt

Whole seeds bloomed in fat and poured over cooked lentils — the tempering that finishes dal across South Asia. Nigella works particularly well in that role because it survives the pour intact, so a soft dish gains texture as well as aroma.

How: In a tempering poured over dal at the end

Add alongside: Cumin, Mustard seed, Fenugreek

Aloo posto is a Bengali staple and one of the clearest demonstrations of what ground poppy seed does: the seed is ground to a paste and becomes the sauce, thickening and enriching a dish that has almost nothing else in it. Potato is bland and starchy and the poppy supplies both body and most of the flavour.

How: Ground to a paste with green chilli for aloo posto; With nigella in a dry potato dish

Add alongside: Nigella, Mustard seed, Turmeric

• Use white poppy seed rather than blue: blue seed turns the dish grey, and the appearance is half of why the swap reads as wrong.

The same Bengali logic applied to a vegetable that absorbs rather than releases. Ground poppy seed thickens the sauce and its oil content enriches aubergine that has already taken up a good deal of fat, which sounds excessive and works.

How: In a posto-style aubergine dish; Ground into a wet masala base

Add alongside: Nigella, Mustard seed, Chilli flakes

Salted spiced fruit is a standing South Asian preparation and black salt is what it is made with. Fruit is sweet and acidic and has no savoury component at all, so a seasoning that supplies salt, sulphur and tang creates a contrast that plain salt cannot — the sulphur reads as savoury depth against the sweetness rather than simply as saltiness.

How: Sprinkled with chilli powder over sliced fruit; In fruit chaat with lime and chaat masala

Add alongside: Chilli powder, Amchoor, Lemon

• Applied to fruit that will stand, the salt draws water out and the pieces soften. Season immediately before serving.