Although they bill themselves as a Thai restaurant, Lan Sang's owners actually hail from Laos, and the menu covers both the Laotian and Thai sides of the border, including the Isan cuisine of northeastern Thailand. The cooking here is refreshingly spicy and uncompromising, with many unusual dishes that are rarely seen in Tokyo.
The generously portioned prix-fixe dinners (Y2500, Y3500 and Y5000) are a convenient way to get started here, but we found some of the best cooking on the a la carte menu, which is worth some serious research. Starting at the top of the appetizer page, we discovered a Northern Thai-style sausage (sai woag) that was one of the finest we've had in Tokyo - an intensely flavorful combination of ground pork, fermented fish paste, garlic, shallots and spices, and of course plenty of hot peppers. Another outstanding starter is the thrillingly spicy Goong Chay Nampla - raw shrimps served with thinly sliced raw garlic, shiso leaf and a fermented fish-based sauce.
At this point it should be clear that an enjoyment of hot spices is a major factor in one's appreciation of the Lan Sang experience. The menu's graphical chili pepper scale will help in case you want a few milder dishes to balance things out (although in this case the term "mild" is relative). There are a couple of homemade sauces that arrive alongside many of the dishes - one is sweeter, the other fishier - and both are sufficiently complex in flavors while delivering a nice chili rush.
Larb is another specialty of Laos and northern Thailand - it's made from ground meat simmered in a broth with spices and mixed with pan-fried grains of uncooked rice that are ground into a fine powder. Here they offer a very tasty version made from pork, beef or chicken, served with a sticky gluttinous rice (kao nyaio) that's eaten with the fingers. Also worth note is the Tom Yam Krunnai, a meaty lemongrass-based soup brimming with tripe. Pretty much everything we've tried here is quite good, and many dishes are worth traveling across town for.
The name Lan Sang means "land of a million elephants" (a nickname for Laos), and the large dining room is filled with numerous bits of elephantine decor. At the very center is a massive six-foot-high carved wooden specimen that must literally weigh a ton. The drinks menu offers Laotian beer, but the Singha is a better bet, or you could opt for the mysteriously popular sparkling wine. Service is friendly (although it can be harried at peak times), and the atmosphere is laid-back and casual. Budget around Y2500-4000 per person with drinks and plenty of food.