First make the sauce. Break the egg into the bowl of a food processor and add the salt, garlic and mustard powder.
Switch the processor on and gradually add the oil through the feeder tube in a thin, steady trickle. When the oil is all in and the sauce has thickened add some pepper and all the other ingredients.
Switch on the pulse button and pulse until all the ingredients are chopped. Tip into a serving bowl.
Put the frying pan on a gentle heat to warm. Wipe the fish and coat with a light dusting of seasoned flour.
Turn up the heat and add the oil. As soon as it is really hot add the skate wings. Reduce the heat to medium and fry for 4-5 minutes on each side.
Put the fish onto warm serving plates and garnish with the parsley. Serve with the tartare sauce and lemon to squeeze over. For a change you can replace the lemon juice and parsley in the sauce with lime and coriander.