Carefully dry the mackerel fillets with a clean cloth and batter with flour. Slice half the
grapefruit and squeeze the other half. Shell the egg and crush with a fork. Mix the
grapefruit juice with the crushed egg and the yoghurt. Season with salt and pepper. Heat slightly stirring softly. Heat the oil in a frying pan and fry the fish on both sides until golden. Transfer to the serving dish and serve accompanied with the sauce and decorate with the minced parsley and the
grapefruit slices.