In Lucknow, Kanpur and across Punjab, the hard green jackfruit that arrives in spring and early summer is cooked like meat in kathal ki sabzi, and the rest goes into a jar of kathal ka achar. The chunks are boiled until just tender, dried, then coated in a fierce mix of mustard oil, fennel, nigella, fenugreek and red chilli, sharpened with vinegar and dry mango powder. The texture is the surprise: firm, fibrous and almost meaty, soaking up spice like a sponge. It goes with puri-aloo at a Sunday breakfast or alongside rajma-chawal. Boiled jackfruit is a low-acid vegetable, so this version is deliberately acidified and lives in the fridge. Common mistake: boiling the jackfruit soft; it then breaks into mush in the jar. Stop when a knife meets slight resistance at the core. It is ready after 3 days, when the chunks have turned tawny all the way through and taste sour, not bland. Keep in the fridge for up to 1 month, under oil, with a dry spoon; discard if mould, fizzing, sliminess or a sour-rotten smell appear. Chef's tip: rub your knife and hands with oil before cutting raw jackfruit, or the sticky sap glues everything.