Peel and finely dice 1 medium-sized red onion. Put it into a stainless steel pan to which you have a lid, pour in 150 ml of red wine vinegar and bring to the boil. Lower the heat and simmer for 10 minutes then set aside, covered by the lid. Cut 2 small pears, skin on, into 1cm dice, discarding the core as you go. Put the pears into the vinegar and onions and cover once more.
Heat an overhead grill. Line a baking sheet with foil. Place 4 fillets of fresh mackerel on the sheet, rub lightly with olive oil and season with salt and black pepper. Cook them under the preheated grill until lightly cooked with their flesh starting to turn gold here and there.
Pick the leaves from a small bunch of parsley, about 8 sprigs should do, and stir them into the pear and onion dressing.
Place the fillets on warm plates, then spoon over the pear dressing. Serves 2.
The pear should retain its crispness, so it remains refreshing. Don’t make it too soon before you eat, otherwise the pear will discolour. Let the mackerel darken and crisp a little around the edges. The thicker flesh in the middle of the fillets should remain soft and juicy.
The mackerel benefits from having a slightly tart, crisp dressing. For a more mellow version, use half sherry vinegar to red wine vinegar. This dressing can also include a few coriander seeds – a teaspoon is enough – or a teaspoon of preserved green peppercorns from a jar, rinsed of their brine.