Kao Soi can be roughly translated to mean “street rice” or “street food”. It’s a common food for common people, served in Northern Thailand especially the Chiang Mai area. It’s usually eaten for lunch.
Remember, Thai food is a regional cuisine. What’s traditional in Bangkok, isn’t traditional in the North or Isaan and visa versa. Those red and green curries that are ubiquitous in Thai restaurants throughout the United States, Australia and Europe are Bangkok curries and are not traditional to other parts of Thailand. Sticky rice is a staple of Isaan and the North, but not Bangkok. Som Tom (a green papaya salad) comes from Isaan. Each region of Siam has its own distinct cuisine.
Northern Thai kao soi is simple and cheap. Start with a mild curry in coconut broth. Add either beef or chicken (often chicken). Put in a fistful of yellow egg noodle. Top with a crunchy noodle. (Like the kind my mother would use when it was “Chinese Night” for dinner and she would open a can of Chung King chop sui and pour it over a bed of this kind of crunchy noodles.) Add a little cilantro…and wha-laa! You’ve got kao soi.
Kao soi is served with a mandatory side dish of fresh shallots, lime and pickled cabbage. Squeeze that lime for all it’s worth into your kao soi. You can eat a couple spoonfuls of kao soi and then a bite of shallot or cabbage. Or, do what I do, just put the whole dish of shallots and cabbage into the kao soi and have at it!
Kao soi is all about textures. You’ve got the soft egg noodle with the crunchy noodles and shallots. The chicken should be “fall-off-the-bone” cooked. The beef too. The pickled cabbage adds another layer of texture.
If you travel to Northern Thailand to see oppressive elephant shows, fake cultural dance exhibitions, or “trek” to Hilltribe villages that decades ago were overrun with crass tourists, then at least have the good sense to sample a little real Northern Thai culture with a bowl of kao soi. It should only cost you about 40 baht.