Add prawn head to saucepan, stir continuously over low heat until cooked, broken.

Temper hot prawn head into egg yolks, then add coconut water, fish sauce, white sugar, and return to saucepan, stir continuously over low heat until just thickened.

Remove from heat, use hand mixer to blend sauce, slowly add prawn oil, then pass through fine strainer, taste, adjust, and reserve in cooler for service.