I've noticed some Laos wince if I order som tam (green papaya salad). That was before I managed to master the Lao name for this dish (which may or may not have originated in Laos -- can't find definitive information on this but if you have some feel free to weigh in): dtam mak huhng.
Dtam mak huhng (please don't call it Lao som tam) has a few elements in common with its Thai cousin: green papaya of course, garlic, peanuts, and chilies.
Lime juice plays a minor role in Lao green papaya salad; in some versions that we've eaten here in Luang Prabang it's barely detectable.
Tomatoes are in there, often two varieties -- larger, pulpy and sweetish, much like Italian plum tomatoes...and petite, super juicy orbs sold on the vine. The latter boast a sour bite.
Whereas Thai som tam is sweet, sour, and spicy, and a little salty, Lao dtam mak huhng veers toward favoring spicy and salty. The saltiness comes from bpadek or fermented fish sauce, which is a close relation to northern Thai blpaa raa.
To be honest, bpadek can be rough going at first. But it lends an incomparable depth to every dish it's added to. Much like shrimp paste (kapi in Thailand, trassi in Indonesia, belacan in Malaysia, and mam tom in Vietnam), it's an ingredient that, while initially quite repellent, is well worth making the effort to get used to.
We reckon that Luang Prabang's best green papaya salad is to be found at Papaya Salad Restaurant, which is unfortunate enough to occupy a shop lot next to the much lauded (and justifiably so) Tamarind. (When we revisited Papaya Salad today the owner was keen to confirm that we understood we were not at Tamarind -- presumably he's had guests get up and leave after comprehending this fact.)
If you're looking to go street style, Papaya Salad prepares its dtam mak huhng at a stall outside the restaurant, and you can order sticky rice to eat with your salad outside.
What makes Green Papaya's version special is the way they prepare the papaya: it's shaved into wide, thin strips rather than grated, so that the fruit-vegetable retains quite a bit of texture and crispiness after it's pounded in the mortar with the other ingredients.
You'll find vegetal and slightly astringent slivers of green globe eggplant in there, and lots of bpadek. (If you just can't take bpadek's sublime stench, say 'Mai sai bpakek/ My Sy Bpah-Dehk' -- and they'll add Thai fish sauce instead.)
It's a truly fantastic plate-full, tomato-y and salty and, if you request yours to be 'Phet phet', very very spicy.
Consider ducking inside the restaurant for a full lunch. The 'fried sour in banana leaf', aka nem (fermented chopped pork) is absolutely heavenly, crisped in a pan and tart with lots of porcine flavor (and admittedly, fat -- but it's pork after all). With a large basket of sticky rice and a serving of dtam mak huhng you're looking at 35,000 kip (about U$4) -- more than reasonable for a lunch for two, by Luang Prabang restaurant standards.
Papaya Salad Restaurant -- one street in from the Mekong, next to Tamarind Restaurant. Green papaya salad stall out front. Daytime.