Wipe fillets with a clean, damp cloth. Mix the other ingredients together with sufficient beaten egg to moisten. Spread a thin layer of forcemeat on each fillet and fold in two. Place the fillets in a fireproof baking-dish and fill up the spaces between with the rest of the forcemeat. Sprinkle lightly with palebrown breadcrumbs, add a few small pieces of butter and bake for about 30 min. in a moderate oven (350° F., Gas 4). Serve in the cooking dish.