One of Chiang Mai’s most famous contributions to Thai cuisine is khao soi, (or soy), noodle soup. The classic version combines two noodle varieties: flat wheat noodles, (tagliatelli-ish in form) and deep-fried crispy noodles, in a spicy coconut chicken curry. The soup is served with a slice of lime, roast chilli paste and pickled cabbage.
Sometimes mistakenly thought to be of Burmese origin, khao soi is actually south Chinese, and was brought into northern Thailand and Burma by Yunnanese Muslim immigrants. So Mae Salong in Chiang Rai, for instance, with its Yunnanese/Kuomintang population, is a great spot to find the original version.