1. Have the heads cut off the fish and the black skin removed. Wash and wipe the soles.
2. With a sharp knife make a cut down the centre of the backbone on one side of the fish, Raise the fillets on this side only away from the bone to form a pocket.Then with the points of scissors cut the backbone through just below the head and above the tail, so that it may be more easily removed after the fish is cooked.
3. Dip the soles in seasoned flour and coat with beaten egg and breadcrumbs.
4. Heat the fat in a large, wide pan until it will brown a 2.5 CM (1in) cube of bread in 1 minute;
5. fry the fish for about 10 minutes and drain on crumpled kitchen paper.
6. Using scissors or a knife, cut the backbone and ease it from the cooked fish.
7. Fill the centre cavity of each fish with maitre d'hotel butter and serve at once.