Kosha mango (a drier form) or mutton curry are Bengali staples reserved for a Sunday or a special occasion, often loved wth steaming rice or a plate of hot and fluffy luchis. Meet another Bengali recipe, posto mangsho, where the mutton curry is given the poppy seed paste treatment: it is made from poppy seeds soaked in hot water for 15 minutes to soften them and then ground with green chillies and salt. This is added to the mutton marinade, which is later cooked in the Bengali favourite mustard oil. Posto is one of the defining ingredients of Ghoti Bengali cooking, as opposed to Bangal households whose roots lie in what is now Bangladesh. Ghotis are known across Bengali culinary culture for their deep attachment to posto, and this affection manifests in a range of preparations like aloo posto, shukto, and the more indulgent posto mangsho. This does not imply that Bangals or Bangladeshis do not cherish their posto; they do and also enjoy an array of dishes, including the three mentioned here. Humans, after all, are hardly homogenous in their food habits. The mutton is marinated overnight, or for at least four hours, for it to tenderise and give you that fall-off-the-bone quality. The marinade of turmeric, red chilli powder, cumin powder, Bengali garam masala, salt, sugar, and mustard oil penetrates the meat well, seasoning it from the inside and tenderising the fibres before any heat is applied. Mutton with fat is preferred for this recipe; leaner cuts cook up drier and lack the richness that makes the gravy so satisfying. Rewaji khasi is something you might want to use at a Bengali butcher shop to refer to mutton with a generous fat cover.