Bangkok Cafe is as authentic as it gets. This tiny restaurant is frequently crammed with native connoisseurs who return for what I assume is an authentic taste of home. Start with steamed prawn and/or beef dumplings, and follow with pad Thai or a suitably strong curry.
You might not eat as cheaply here as you would on Khao San Road but rest assured that €10 to €15 will ensure you can dine like a god. Guzzle a few frosty bottles of Singha to keep cool and whatever you do, trust your server when they describe a dish as being “quite spicy.” This is the real deal.