Before antibiotics existed, well-known Bengali physicians — including Dr. B. C. Roy — reportedly prescribed mishti doi to typhoid patients to help them recover their B-vitamins, decades before anyone called it a health food.
Milk is boiled down and sweetened with jaggery or sugar, then set to ferment overnight in a small earthenware pot whose porous clay walls slowly wick away moisture, thickening the yogurt into a dense, caramel-toned set custard. Sweet shops across Kolkata sell it by the pot, straight off the fermenting rack.