Peel and rinse papaya. Quarter lengthwise. Discard seeds. Trim inner surface. Cut crosswise 1½ cm thick.
800 g half-ripe papaya
Peel prawns, leaving tails on. Devein and rinse. Reserve shells and heads for making stock.
350 g prawns
Rinse threadfin bones twice.
80 g salted threadfin bones
Peel shallots and wash. Chop roughly.
80 g shallots
Rinse candlenuts and red chilli.
12 g candlenuts (3 pieces), 1 red chilli
Bring prawn shells and heads, salted fish bones and water to a boil. Simmer gently, covered, for 5 minutes or so.
900 ml water
While stock is simmering, rinse dried prawns and dry-fry till fragrant.
40 g dried prawns (¼ cup)
Grind or blend dried prawns, shallots, candlenuts, chilli, and white peppercorns finely.
1 tbsp white peppercorns
Remove and discard prawn shells and heads from stock with a slotted spoon. Add ground paste. Continue gentle simmering for 10 minutes. Add papaya and bring back to a boil. Simmer till almost tender, 3-4 minutes depending on how ripe papaya is. Do not overcook or papaya would turn mushy.
Turn off heat. Let soup sit 10 minutes, covered, to develop flavours.
Reheat soup till gently simmering. Taste and season with sugar to taste, about ½ tsp. Add prawns and heat till just pink and opaque. Do not overcook.
sugar to taste
Serve soup hot, accompanied by sambal belachan and calamansi lime juice as a dip.