Mishti Doi
Mishti doi (literally "sweet yoghurt") is the great quiet sweet of Bengal: not as showy as rasgulla, not as rich as sandesh, but possibly the most loved of all. The technique is built on three reductions. First, the milk is boiled down by about a third to concentrate its sugars and proteins, which makes the eventual yoghurt thick enough to hold a spoon upright. Second, a portion of jaggery (date palm jaggery, nolen gur, in winter; cane jaggery, akher gur, year-round) is melted and cooked further until it caramelises to a deep amber. This is the move that defines mishti doi, it isn't simply sweetened yoghurt, it is yoghurt sweetened with caramelised jaggery, and the colour, the toffee notes and the depth come entirely from that caramel. Third, the seasoned milk is poured into porous unglazed clay pots (matka or bhar) and inoculated with a spoonful of live yoghurt before being left to set in a warm place for 8-12 hours. The clay pot is not decorative: it absorbs whey through its walls, producing a denser set than a glass or plastic container ever can, and it cools the doi by evaporation so it stays at fridge temperature even on a Kolkata summer afternoon. Mishti doi is the closer to a Bengali feast, after fish, after rice, after rasgulla even, eaten with a small spoon directly from the pot. It is also a winter speciality when made with nolen gur, the fragrant first-tap date palm jaggery that arrives in Bengal markets in December and disappears by February; that version, payesh doi or nolen gurer doi, is one of the great seasonal sweets of the subcontinent.