In essence, it might be the perfect January dish.
With a veil of healthfulness, but still comforting, warming, and soothing, cod in tomato sauce hits all the spots that need to be scratched at this time of year. The silky fish, cooked so gently, until it just starts to flake in the sauce, lends a richness and a sweet hint of the sea to a plain tomato sauce, like the most basic one that I wrote about here.
Truth be told, the basic approach I take is to get the sauce just how I like it, then at the last minute, add the fish and simmer, covered, at the lowest bubble. The possibilities are endless—yes, you can certainly start from scratch, but a cup of leftover sauce in the fridge is also a good starting point. It can be as thick as a sauce or as thin as a broth; your sauce, if only starting from said cupful, can be stretched with some white wine or even a little chicken or clam broth. A hefty pinch of saffron, if you have it, can transform it from leftover to a bona fide feast in its own right; but some chopped fresh basil or parsley, or a handful of rinsed capers, is also quite nice. I am happy to eat it on its own, but in the interest of making it not so difficult a family meal, I usually put out some buttered orzo, fregola, Israeli couscous, freekah, or even barley, on the side.