Trim and pin bone the fillets. Season on both sides. Heat a frying pan until hot and add a splash of olive oil. Sear the fish skin side down until golden. Turn the fish and remove the pan from the heat to finish cooking the fish.
Peel the carrots and the celery. Peel and finely slice the red onion. Top and tail the radishes and then cut into quarters. Slice the carrots and celery thinly on the angle. Carefully chop the dill.
Place the fennel seeds, black pepper corns, bay leaves, salt, vinegar and sugar into a pan. Warm to dissolve the sugar and then add the carrots, red onion and celery and bring to the boil. Simmer for 5 minutes, remove form the heat and then leave the vegetables to cool down in the pickling brine. Add the radishes at this stage. Once cool, drain off the pickling liquid and stir the chopped dill through the vegetables.
Finely grate the horseradish and zest the lemon. Mix into the crème fraiche with the cayenne pepper. Add a pinch of salt if needed.
Place a neat pile of the vegetables in the centre of the plate and lay the fillets of mackerel crisscrossed on top. Finish with a spoonful of horseradish crème fraiche.
«Use seasonal vegetables depending on the time of year you are preparing the dish.»