To make the sweet & sour beetroot, mix all the ingredients, except the beetroot, with 125ml water in a medium pan and bring to the boil. Take the pan off the heat and leave to cool. Drain and rinse the cooked beetroot, then slice half into thin rounds, cutting the rest into larger wedges for a contrasting texture. Once the pickling liquor is completely cold, pour into a large jar, add the beetroot and chill overnight.
The next day, brush the mackerel all over with the soy sauce and leave to marinate for 20 mins while you make the dressing. Whisk together the wasabi and crème fraîche, seasoning to taste. Heat your grill to its highest setting.
Remove the beetroot from the pickling liquor with a slotted spoon and divide evenly between each plate. Layer over the shallot, pickled ginger and toasted sesame seeds, then scatter over the chives to create the salad. Layering the salad creates a professional finish.
Put a wire rack over a baking tray and brush with the oil. Put the fillets on top of the wire rack and grill the fish, skin-side up, for 2-3 mins until the skin is charred and the fish is lightly cooked. If you want to char it further, use a blowtorch (see my tip below).
To serve, place the fish on top of each salad with a spoonful of the dressing. For added wow factor, drizzle the oil around the salad, along with a little of the pink pickling liquor from the beetroot, then serve immediately.