Look for the small shop to the right of the main fort entrance. Like others said this is now called "Lassi shop". This is the original shop and the one you may have seen on documentaries. Now someone else has payed more money for the title of "government approved" so they can't put that on the sign but its all good, the other shop has been making people sick.
I tried the lassi and took some cookies... they hit the spot... but take it easy because it is strong!