In a small bowl, combine the palm sugar, fish sauce, lime juice, and tamarind water to create a som tum salad dressing. Try it – it should taste all at once sweet, salty and sour – then adjust any of the ingredients to suit your taste, and set aside.
In a large wooden mortar and pestle, pound the garlic with the salt, then add and pound the peanuts and dried prawns to a coarse paste.
Add the lime quarters to the mortar, bruising them with the pestle, then add the cherry tomatoes and beans, pound lightly, and push to the side.
Add the bird’s eye chillies, pound lightly, barely crushing them; the more they’re pounded, the hotter the dish will be, so pound away if you can handle the heat.
If your mortar is large enough, add the green papaya now, lightly bruise it with the pestle, and with the other hand use a large spoon to turn and toss the salad. Add the dressing you made earlier and combine everything well. It should taste sweet, sour, salty, and spicy-hot.
If your mortar is not big enough, transfer the first lot of pounded ingredients to a salad bowl, then bruise the papaya in the mortar with the pestle, add the seasoning and combine, then then transfer that to the salad bowl, and combine everything well.
Serve with steamed rice, raw vegetables such as green beans and cabbage leaves, and sprinkle additional crushed peanuts over the salad.