Still in the Thanon Tanao area of Banglamphu, virtually across the street from K. Phanich and Nom Jo (I told you there's a lot of good stuff to eat here), exists a second-generation shop that specializes in making one product: paa thong ko. Essentially deep-fried bits of dough, it's a simple dish, and the owner has been making them in the same place for fifty years, taking over from his parents after they were too old to run the business.
The paa thong ko are served with a sweet milk-based dipping sauce flavoured with (and turned green by) bai toey, pandanus:
Paa Thong Ko Sawoey (Google Maps link)
540 Thanon Tanao
02 222 2635