Hot-Smoked Mackerel with Beetroot, Horseradish and Watercress

Ingredients

• 4 whole mackerel, gutted and butterflied (ask your fishmonger)
• 1 litre cold water
• 80g fine sea salt
• 60g soft light brown sugar
• 1 tbsp black peppercorns, cracked
• 2 bay leaves
• zest of 1 lemon
• 2 large handfuls oak chips, soaked in cold water for 30 minutes then drained
• 1 tbsp soft light brown sugar (to scatter on the chips)
• 200g soured cream
• 3 tbsp finely grated fresh horseradish (or 2 tbsp hot horseradish from a jar)
• 1 tsp Dijon mustard
• 1 tbsp lemon juice
• small handful dill, finely chopped
• sea salt and black pepper
• 500g cooked beetroot (vac-packed, not in vinegar), cut into wedges
• 1 small red onion, very thinly sliced
• 2 tbsp cider vinegar
• 1 tbsp extra virgin rapeseed oil
• 1 tsp runny honey
• 1 tsp caraway seeds, lightly toasted
• 1 small bunch dill, roughly chopped
• 100g watercress, thick stems trimmed
• 1 Granny Smith apple, cored and cut into matchsticks
• juice of ½ lemon
• good glug of extra virgin rapeseed oil

Method

1. Make the brine first so the fish has time to cure. Dissolve the salt and brown sugar in the litre of cold water along with the cracked peppercorns, bay and lemon zest — stir until you can't feel grit on the bottom of the bowl. Lay the butterflied mackerel skin-side up in a deep tray, pour the brine over so they're fully submerged, and refrigerate for 45 minutes. Any longer and the flesh turns hammy and over-salted; mackerel is oily and takes salt fast.
2. Lift the fish out, rinse briefly under cold water, then pat completely dry with kitchen paper and lay skin-side down on a wire rack. Leave them uncovered at cool room temperature for 30 minutes — you want the surface to feel tacky and slightly glossy when you touch it. This is the pellicle, and it's what the smoke actually sticks to. Skip this step and the smoke just rolls off.
3. Set up your smoker. For a hob smoker: line the base with foil, scatter the drained oak chips and the tablespoon of brown sugar across, and set the rack above. For a kettle BBQ: bank the coals to one side, get them ashed-over and grey, then scatter the drained chips directly onto them and put the grate in place. You're aiming for a chamber temperature of 90–110°C — hot enough to cook the fish through, gentle enough to keep it silky.
4. When the chips start sending up steady wisps of pale blue smoke (not thick white billows — that's acrid and will taste of ashtray), lay the mackerel skin-side down on the rack on the cool side of the BBQ, or in the smoker. Cover with the lid, vents cracked just a little, and smoke for 35–45 minutes. The fish is done when the flesh has turned from translucent grey-pink to opaque bronze and flakes cleanly when nudged with the tip of a knife at the thickest point near the head. Lift them off and let them sit on the rack for 10 minutes — they firm up as they cool and become much easier to lift whole.
5. While the fish smokes, build the horseradish cream. Stir the soured cream, grated horseradish, Dijon, lemon juice and dill together in a bowl with a good pinch of salt and plenty of black pepper. Taste — it should make your nose tingle. If it doesn't, add more horseradish; the heat fades within an hour of grating, so be generous.
6. Make the beetroot salad. Whisk the cider vinegar, rapeseed oil and honey together in a bowl, then toss through the beetroot wedges, sliced red onion, caraway and most of the dill. Let it sit for at least 10 minutes — the onion mellows and turns rosy from the beet juice, and the whole thing tastes brighter for the rest.
7. Just before serving, dress the watercress and apple. Toss the cress and apple matchsticks with the lemon juice, a glug of rapeseed oil and a pinch of salt — do this at the last minute so the leaves stay perky and the apple stays crisp.
8. Toast the rye bread lightly and butter it generously while warm. Spread a spoonful of horseradish cream on each slice, lay over a piece of mackerel (skin on or peeled off, your call — the skin lifts away easily once smoked), pile beetroot to one side and watercress-apple on the other. Finish with extra horseradish grated over the top, a squeeze of lemon and a pinch of flaky salt.