Lemon pickle is the one achar that North Indian grandmothers hand over without a speech, because there is almost nothing to it: lemons, salt, a few spices, a jar and patience. No oil goes in. The quartered lemons sit in salt and their own juice, in a sunny window or on the roof, and over three or four weeks the peel turns soft, translucent and brown, and the juice becomes a thick, sweet-sour syrup. This version is the khatta-meetha kind, with sugar, ajwain, black salt and chilli, loved with parathas, khichdi and as a cure for an upset stomach; leave out the sugar and double the chilli for the salty, sharp version. Use thin-skinned, juicy lemons (kagzi nimbu) and wash and dry them thoroughly. Common mistake: being impatient; the peel is bitter and hard until it has fully cured, so wait until it squashes easily. Keep the pieces pressed under the juice, use only a dry spoon and discard the jar if mould appears. Chef's tip: shake the jar every day rather than opening it; less air and fewer spoons mean less risk of spoilage.