Slice the kernels from a head of sweetcorn and drop them into the pan. Roughly chop two spring onions and a small bunch of parsley, and stir them into the soup carefully, without breaking up the fish, then serve as soon as the corn is tender.
You could use one of the ready-prepared assortments of fish meant for fish pie if it is more convenient. The soup is a calming, delicate version, but sustaining enough to be a light main dish. It is important not to stir the chowder too much as it cooks, which would result in the fish breaking up.
I sometimes like to add a handful of mussels or clams to the soup once the fish has almost reached tenderness. Finely sliced leeks can work well instead of the onion. To give the soup a sweeter note, cook the onion or leek in a little butter and oil until it is soft, before adding the milk. You could stir in a little tarragon or dill, finely chopped, into the soup near the end of the cooking time.
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Nigel Slater: 'Stir in tarragon or dill, finely chopped, near the end of the cooking time.' Above: his quick fish chowder recipe. Photograph: Jonathan Lovekin for the Observer