Make sure all the bones are removed from the fish. Use kitchen tweezers to pull out any pin bones.
Slice each fillet to required thickness.
Cut some paper-thin slices of lemon and lay them on each slice of plaice (this is not to be eaten just to give a slight hint of lemon to the fish).
Mix together the ginger, garlic, shallot, chilli and sesame oil in a small bowl, add a good glug of Japanese soy sauce and a sprinkling of brown sugar.
In a separate dipping bowl mix together the grated horseradish with the mustard powder and pour in a little soy sauce.
In another dipping bowl, mix together some wasabi paste and soy sauce.