Cover the mustard seeds with water and bring to the boil. Blanch them in cold water, strain then repeat the process of boiling them and blanching them four more times.

Slice the courgette into thin slices and put into a sterilised jar along with the chilli and the cooked mustard seeds. Mix the sugar and vinegar together until the sugar dissolves then pour it into the jar with the courgettes, mustard seeds and chilli. Put on an airtight lid, give it a good shake and place in the fridge for at least two weeks before using.

Whisk the cream and horseradish sauce together and season with two pinches of sea salt and two pinches of ground white pepper.

Season the mackerel fillets with a layer of fine sea salt and let them sit at room temperature for 15 minutes. Place them on a metal tray, then, using a blowtorch, scorch each fillet until slightly charred and cooked medium. This will take about two minutes per fillet. Squeeze lemon juice over them all. To serve, drizzle the horseradish cream onto each plate, add a spoonful of pickled courgette, two fillets of mackerel and some dill to garnish.