The story starts at Nizam's near New Market in the 1930s. Kebabs came off a skewer, the kathi, and were eaten with paratha; the innovation was to wrap one inside the other so a clerk could eat it walking and hand back nothing.
The egg came later and is now non-negotiable for most people. A paratha goes on the tawa, an egg is broken over it and spread thin, the whole thing is flipped so the egg cooks into the bread, then it takes the meat, raw onion, green chilli and a squeeze of lime.
Order it by construction, not by name: single egg double mutton, double egg chicken, and so on. Anywhere that asks whether you want it wrapped in paper is doing it right.
It has travelled badly. What is sold as a kathi roll elsewhere in India is usually a wrap with a Kolkata name on it.
