For dressing, combine tamarind pulp and 100ml boiling water in a bowl and stand for 30 minutes. Place dried shrimp in a mortar and, using a pestle, pound until finely ground. Place ground shrimp, galangal, shrimp paste and palm sugar in a heavy-based saucepan and cook over medium heat for 5 minutes or until sugar melts.
Increase heat to high and simmer for 5-6 minutes or until fragrant. Add tamarind mixture and fish sauce and return to the boil, then remove from heat, strain through a fine sieve and cool. Stir in enough cold water to achieve the consistency of pouring cream. Makes about 2/3 cup. Dressing will keep, refrigerated in an airtight container, for up to 3 weeks.
Using a small, sharp knife, remove rind from lime, leaving a small amount of flesh on the skin, then chop rind into 2mm pieces.
3 Place grated coconut on an oven tray and roast at 180C for 15 minutes, stirring frequently until golden.
4 Char-grill or barbecue prawns over medium-high heat until just cooked through. Place 4 betel leaves on each plate. Combine peanuts, shallots, chillies, chopped lime rind, coconut and herbs in a bowl, then add 2 tbsp dressing, or to taste, gently combine and divide salad among leaves. Top each leaf with a cooked prawn and serve immediately.