1. To obtain assam or tamarind liquid, squeeze out the pulp in a little hot water then pass through a sieve to strain the juice. If you can't find tamarind pulp use 3 tablespoon tamarind mix, dissolve in 1 cup of water. You can also use tamarind paste.
2. In a mixing bowl, combine the tamarind liquid, sugar and soy sauce.
3. Marinate prawns in this mixture for at least 2 hours in the fridge.
4. Heat oil in a wok over medium to low flame. Add the prawns together with the marinade and fry until slightly burnt and aromatic. Season with pepper to taste. Serve immediately.