For the prawns, in a bowl, mix together the egg white, cornflour, sherry and salt and freshly ground white pepper.
Add the prawns, stir to coat and set aside for 30 minutes to marinade.
Suspend a steaming basket over a pan of simmering water. Add the marinated prawns, cover and steam for 6-7 minutes, or until pink.
For the oolong tea sauce, place all of the oolong tea sauce ingredients into a pan and bring to the boil, stirring well. Season, to taste, with salt and freshly ground black pepper. Boil for one minute, then remove from the heat.
To serve, mix together the cooked rice and peas and divide the mixture equally among four serving bowls. Place a few prawns on top of each portion. Spoon over the oolong tea sauce and garnish with the chopped mint leaves.