Mix the marinade from the ingredients listed. Place the fish fillets in a deep dish and pour it over the fish. Leave to marinate for a few hours, turning the fish over from time to time. Drain and dab with a dishcloth. Flour, pass through the egg beaten with a little salt and then turn to the other side in the breadcrumbs sifted through.
Heat half the butter with the oil in a large frying pan and brown the perch fillets well in it on both sides.
Drain and arrange on a heated roasting pan.
Add the remaining butter to the roast stock, add the sage leaves, mix well and pour over the fish fillets.