There are (relatively) complicated ways to make fishcakes, like a method I described some years ago , which involved onions, celery and eggs, and which substituted celery root for the usual potatoes. Those are delicious, and I make something like them every now and again.
Yet the basic fishcake – essentially, cooked fish and boiled potatoes smashed together and fried – is a lovely thing, and Jackie and I had a few of them for dinner the other week, with what in her native Britain is called parsley sauce: béchamel containing lots of chopped parsley. It almost goes without saying, however, that I tinkered with both the fishcakes and their sauce: only a little, but it made a difference by lending brightness to a dish that cannot always be said to sparkle.
What I did was add capers to the fishcakes and freshly grated horseradish to the sauce. Neither was a stretch: Capers are much used with fish of all kinds, and horseradish is an established partner of cream sauces hot and cold.
The fish came from the freezer. I am sometimes ribbed about my restauranty practice of trimming fish into neat portions of nearly uniform thickness. I do this in part because such pieces cook more evenly, but also because I like having the off-cuts in the freezer for things like ... fishcakes. In this case, the fish was hake, which is related to cod and haddock; it is just about ideal for this recipe because it breaks up easily into flakes and because it has enough flavor to fight its way through the potatoes but not so much that it swamps them. Like cod, it benefits mightily from being salted half an hour before cooking, which improves texture and flavor. Here, I use thinner pieces from the tail end; if you are using plumper fillets, add half a minute to the initial simmering time.
My proportion of potato to fish (a little heavy on the potatoes) is a family preference; there’d be no harm in using equal weights of these two principal ingredients, but I don’t recommend tipping the balance too far in favor of the fish: Fishcakes are as much a potato dish as anything.
Everything apart from the final frying should be done in advance to give the fishcakes time to firm up in the refrigerator.
Pat the fish dry and generously salt it; leave in the fridge, covered with paper toweling, for 20 to 30 minutes, then briefly rinse and place into a saucepan. Cover with about 2 cups of lightly salted whole milk, add a sprig of thyme (optional) and bring to a simmer over medium heat. Lower the heat and simmer for 30 seconds (one minute for thicker pieces), remove the pan from the heat and cover. Leave for 5 to 8 minutes; the fish will finish cooking in the gradually cooling milk. Remove the fish to a bowl to cool. Save the milk: it will soon become sauce.
Meanwhile, peel and halve the potatoes, add to a pan with cold salted water to cover. Bring to the boil, lower the heat to a vigorous simmer, cover the pan and cook until tender, 15 to 25 minutes depending on the potatoes and the size of the pieces. Drain and place in the bowl with the fish to cool until they can be handled.
Use your hands to squeeze and smash the fish and potatoes. The potatoes should be partly pureed and partly crushed into small fragments; the fish flaked small – and use this opportunity to feel around for any bones that may have strayed into the bowl. Add the capers. Season with salt and (modestly) with pepper. Do not form the cakes yet: you need to make the sauce first.
So, make the sauce: In a clean saucepan over medium-low heat, melt the butter and whisk in 2 Tbs flour to form a roux. Cook, whisking almost constantly, for a minute, then gradually whisk in the milk in which the fish had been cooked (if you think of it, ladle it into the roux through a strainer to catch the thyme – if using – and any fish fragments). Bring to the boil and simmer for five minutes; the sauce will be thickened but fluid.
Add two tablespoons of this sauce to the fish-potato mixture and stir well to combine. Using a fourth of the mixture, form a disc about one inch thick. If it does not hold together, return it to the bowl and mix in two tablespoons of breadcrumbs; leave for a couple of minutes, then try again. The fishcakes should be fragile, but they need to hold up to the minimal stress of breading and frying.
Now that the mixture has the right consistency, form it into four one-inch-thick discs, compressing them with your hands; refrigerate them on a plate for at least half an hour before breading.
Meanwhile, zip up the sauce with the grated horseradish (I use a microplane rasp to achieve a very fine consistency, but the finest screen on any grater will be okay) and leave it to steep. (Taste to see if you want to add more horseradish.)
Bread the fishcakes: sprinkle with flour, gently turn in the beaten egg, then in the breadcrumbs. Strew a handful of crumbs onto a plate, set the breaded fishcakes on this bed of crumbs, then sprinkle them with additional crumbs. Refrigerate until it’s nearly dinner time.
Heat 1/4 inch of oil in a 10- or 11-inch frying pan over medium heat. Test the temperature by adding a fragment of breading; if it sizzles gently, proceed; if it browns instantly, let the oil cool down before adding the fishcakes. They need to brown fairly slowly so that the cold interior will warm through.
Carefully add the fishcakes to the oil and fry until golden brown on one side. Gently flip and cook until the second side is done. You can flip once more if you’d like Side A to be browner.
While the fishcakes are frying, reheat the sauce and add the chopped parsley; check for seasoning.
Drain the fishcakes on paper towels and serve with the sauce.
You may wish to finish these fishcakes or the sauce with a spritz of lemon juice. There’s no good reason you shouldn’t, but the capers and horseradish should do the job on their own.