Season fish with peppercorns and salt. Mix egg yolk, 2 tablespoons clarified butter and juice of 1/4 lemon together. Brush yolk mixture onto fish and press nuts into each side. Place 2 tablespoons clarified butter in frypan. When hot add fish and fry 3 minutes each side, add heated sherry and set alight. Add chopped parsley stalks. Place fish on serving dish. Add 1 tablespoon butter and extra lemon juice to frypan, pour sauce over the fish.