by Mitch Tonks from Fish Easy (Pavilion Books)
Photography, Chris Terry
50g/2 oz/4 tbsp butter, plus a little extra for topping the potatoes
olive oil 2 onions, thinly sliced 4 salted anchovy fillets 4 potatoes, thinly sliced 8 mackerel fillets, pin-boned (you can ask your fishmonger to do this)
1 tbsp fresh thyme leaves
freshly ground black pepper
dressed green leaves to serve
Preheat the oven to 220C/425F/gas mark 7.
Melt half the butter with a little olive oil in a pan over a low heat and fry the onions until soft and golden – about 8 minutes.
Add the anchovies and cook until they have dissolved, then remove the onions and anchovies and set aside.
Add a little more oil and the remaining butter to the pan and cook the potatoes in the same way until crisp on the edges and just cooked – about 6 minutes.
Place half the potatoes in a layer in a roasting pan, then lay the fish fillets on top and sprinkle with thyme and pepper.
Lay the onion and anchovy mix on top, then finish with the remaining potatoes.
Add about 150 ml/5 fl oz/2⁄3 cup water, then dot with butter and bake for 10–12 minutes, until the mackerel is cooked and the potatoes are crisp.
Serve with green leaves dressed with a light vinaigrette.
AT THE FISHMONGER Ask your fishmonger to pinbone 8 mackerel fillets.