1. Soak dried shrimp in water for 5 minutes to soften. Then drain.
2. To shred papaya, use a knife to ‘tap’ the papaya until lots of little shards start falling off. Use the knife to shave off slivers of the papaya. Then start the tapping and shaving again. Alternatively, use a julienne vegetable peeler.
3. In a large som tum mortar, place garlic, dried shrimp, peanuts and chillies. Use a wooden pestle to bruise ingredients. Add 2 handfuls of shredded papaya, 2 tbsp fish sauce and a teaspoon of sugar. Use a spoon and the pestle to mix and bruise the salad.
4. Add another handful of papaya and another tablespoon of fish sauce and another ½ teaspoon of sugar. Bruise ingredients again. Then add tomatoes and snake beans.
5. Give the mixture one final bruising with the pestle. Then toss through lime juice and season to taste with more fish sauce if needed.