The mackerel at the market this morning were fat and firm and still had that iridescent shimmer, blue-green-silver, like petrol on a puddle. That's how you know. When they're fresh, really fresh, they look like they're still moving. I bought four and carried them home in paper.

Mackerel wants heat and sharpness. The oiliness of the fish is the thing people flinch at, but it's also the thing that makes it worth cooking. A hot grill crisps the skin and renders some of that richness out, and a smear of mustard cuts through what's left. English mustard for the kick, Dijon for the smoothness. Lemon over the top, enough to make your fingers sting. The whole thing takes less time than setting the table.

This is a June supper, or July, when mackerel are running and the evenings are long enough that you're still eating in daylight. I wrote it down in the notebook years ago: mackerel, mustard, lemon, Tuesday. It's become one of those meals I come back to when I want something that tastes clean and direct, like the sea got involved in dinner. There are few better feelings than putting a plate of grilled fish in front of someone on a warm evening and watching them reach for the bread before you've sat down.

A recipe is a conversation, not a contract. If you prefer one mustard to the other, use that. If you've got a handful of capers or some cornichons, chop them through. The fish is the thing. Get the best you can.