Fillets of Turbot Topped with Grain Mustard

The delicate butter sauce for this dish contrasts well with the meaty texture of the turbot and the coarse-grained mustard topping, giving an easy to prepare and interesting main course dish. Be sure to use a grain mustard; it tends not to be so fiery as most others and also has a nicer texture. Brill or halibut would make good substitutes for the turbot.