Heat vegetable oil in a deep-fat fryer to 190°C.
Dust the oysters and prawns lightly with plain flour.
Whisk sifted flour, cornflour, salt, and sparkling water together to form a lumpy batter.
Dip an oyster into the batter and fry for 2-3 minutes until golden.
Drain the fried oyster on kitchen paper and repeat with remaining seafood.
Blend egg yolks, salt, pepper, vinegar, chillis, and yuzu juice in a food processor.
Emulsify by slowly blending in the oil and reserved oyster juice until a thin mayonnaise forms.
Pile seafood on a platter, drizzle with dressing, and garnish with coriander cress.