The tandoor is a clay oven, buried or standing, heated with wood or coal, in which bread is slapped onto the inner wall and meat is lowered on skewers.
It is very old. Tandoor-shaped ovens have been excavated at Harappan sites, which puts the technology in this region four thousand years back.
In a Punjab village it was the sanjha chulha, the shared oven, and it was communal for fuel reasons. In a restaurant it became the basis of an entire cuisine.
Tandoori cooking as a restaurant style was developed at Peshawar before 1947 and taken to Delhi by refugees, principally at Moti Mahal, where tandoori chicken, butter chicken and dal makhani were created in the late 1940s.
The food the world knows as Punjabi is a refugee restaurant cuisine roughly seventy-five years old, built on an oven four thousand years old, and it is not what most Punjabi villages eat.
It works because clay holds heat and gives it back. The wall reaches a temperature no domestic oven does, the bread is cooked in under a minute, and the fat coming off the skewers burns on the coals and smokes the meat hanging above it, which is where the taste actually comes from.
The village oven was not for everyday bread. Roti was made on a tawa at every meal. The tandoor came out for a quantity, for a wedding, for the winter months when a shared fire is worth walking to. Calling it the everyday oven of Punjab has it backward.
Kundan Lal Gujral, Kundan Lal Jaggi and Thakur Dass came out of Peshawar and put a Peshawari oven into a restaurant at Daryaganj. Butter chicken exists because tandoori chicken dries out and somebody had to do something with the previous day's. The most famous dish in Indian cooking is a way of using leftovers.
Archaeological evidence for tandoor-type ovens at Harappan sites.