Why mackerel and rhubarb work together

Mackerel is one of the most underrated fish in British waters. It is rich, oily and full of flavour, but that richness can overwhelm if you serve it with anything heavy. Rhubarb, by contrast, is sharp, tart and bright. When you cook it down with a modest amount of sugar, it becomes a savoury compote that cuts through the oil like a knife. The two ingredients also share a season. Outdoor rhubarb starts in April, just as mackerel begin to arrive in numbers off the coast. Forced rhubarb, available from January, is sweeter and more delicate, but it has enough acidity to do the job. This is not a dessert sauce. Think of it as a British take on the sharp fruit condiments served with rich fish elsewhere.

Choosing and preparing the mackerel

Fresh mackerel should smell of the sea, not of ammonia. The flesh should be firm and springy, and the skin should be glossy with a clear, bright pattern. If you buy whole fish, ask your fishmonger to fillet it for you. If you fillet it yourself, work from tail to head with a sharp knife. Run a finger along each fillet to check for pin bones, pulling out any with tweezers.

Before cooking, the most important step is drying the skin. Pat the fillets with kitchen paper, then leave them skin-side up in the fridge for ten minutes while you make the sauce. Moisture is the enemy of crisp skin. Just before they go into the pan, season the flesh side with sea salt flakes and black pepper. Salt the skin lightly as well, but only at the last moment, as salt draws out water. If the fillets are very thick, make two or three shallow slashes through the skin to help the fat render and prevent curling.

A sharp rhubarb compote

This makes enough for four fillets. You need 400g of rhubarb, trimmed and cut into 3cm lengths. Use 60g of golden caster sugar for forced rhubarb or 80g for outdoor rhubarb, which is tarter. Put the rhubarb in a saucepan with a tablespoon of water and a good pinch of salt. Add a strip of orange zest, a star anise, or a thumbnail of fresh ginger if you like, but keep the flavours clean. Cook over a low heat for 8 to 10 minutes, stirring only once or twice, until the rhubarb collapses at the edges but still holds some shape. You want a spoonable compote, not a jam.

Finish with a teaspoon of red wine vinegar or balsamic vinegar. This lifts the sharpness and stops the compote tasting flat. Taste: it should be tart enough to make you wince, as that is what balances the fish. Let it cool to room temperature. It will keep in the fridge for a week. Serve it cold or barely warm, never hot, so it does not wilt the crisp skin.

Pan-frying skin-side down

Use a heavy-based frying pan, preferably stainless steel or cast iron, though non-stick is more forgiving. Put it over a medium-high heat and add a thin film of rapeseed or groundnut oil. Wait until the oil shimmers. Lay the fillets skin-side down, away from you. Press each fillet gently with a fish slice for 20 seconds. This stops the skin from curling and ensures full contact with the pan.

Now leave them alone. The skin will initially stick, then release naturally as it crisps. Cook for 3 to 4 minutes for a typical fillet, depending on thickness. You can tell they are ready to turn when the flesh has turned opaque two-thirds of the way up the side and the skin is golden and crisp. Turn carefully with a fish slice and cook for just 30 to 60 seconds on the flesh side. The fish should be cooked through but still moist. If you have a thermometer, aim for 55°C to 60°C in the centre. Rest the fillets on a warm plate for two minutes, skin-side up, so the skin stays crisp.

Serving and seasonal variations

Serve the mackerel skin-side up on a spoonful of rhubarb compote. Add buttered new potatoes, or crush them with a little olive oil and sea salt. Spring greens, watercress, or a sharp radish salad work well. A slice of good bread is not optional, as you will want to mop up the juices. Do not drown the fish in sauce. A generous tablespoon per fillet is plenty.

If rhubarb is out of season, you can use gooseberries, redcurrants, or a sharp Bramley apple compote. In autumn, a little blackberry works too. But the spring version, with forced rhubarb and the first mackerel of the year, is the one worth waiting for. Any leftover mackerel flakes beautifully into a salad with cold new potatoes and a mustardy dressing.

The everyday skills behind the dish

This recipe teaches three things that will improve all your cooking. First, dry your ingredients before you fry them. Whether it is fish skin, mushrooms, or a piece of chicken, surface moisture steams rather than browns. Second, learn to judge pan heat by sound and sight. A faint sizzle means the pan is not hot enough; a confident roar means it is. Third, balance fat with acid. Oily fish, roast pork, and rich cheeses all benefit from something sharp. A compote like this one is a template: fruit, a little sugar, a pinch of salt, and a splash of vinegar. Once you have made it a few times, you will stop measuring and start tasting. That is when home cooking becomes truly practical.