Halibut Fillet with Aromatic Vegetables and Soft Herbs

This dish makes stars of the usual supporting cast of onion, carrot and celery, using them as the main ingredients of the sauce, which is rich and delicate at the same time. The courgette is there mainly for the colour, and its mild flavour won’t interfere with the rest. This is a good sauce for other softfleshed fish like sole and plaice, as the vegetables have a pleasing firmness.