Place all ingredients (including the oyster ‘juice’) except the oil into a blender and blend until smooth. Slowly pour in the grape seed oil to emulsify the mix; similar to a mayonnaise.
Place in a squeezy bottle and set to one side.
For the tartare
Dice up the mackerel fillets neatly and place over ice to remain chilled.
Mix the diced mackerel with the shallots, chives, crème fraiche, lemon and white soy until combined.
Place seasoned mix into a ring in the middle of a plate.
Dress the top of the tartar with 5 dots of the oyster cream. Then cut the apple into small batons and place on top of the oyster cream. Finish the dish with the shiso cress, placing five of each colour on top of the apple.