Preparation

• 1
  Peel and slice the white beetroot into wafer thin rounds using a mandolin; watch your fingers! Repeat with the red beetroot and place into 2 dishes.
• 2
  Pour the rice vinegar and cold water into a small saucepan. Add the sugar, salt, bay leaves, peppercorns and crushed chillies.
• 3
  Bring to the boil and simmer gently for a two minutes. Pour the pickling liquid over the dishes of beetroot, leave to cool then refridgerate overnight
• 4
  To make the horseradish cream, peel and finely grate the horseradish root, then whip the double cream until it begins to thicken.
• 5
  Combine the grated horseradish, mustard and a tablespoon of lemon juice with the cream. Leave to chill in the fridge.
• 6
  Squeeze a little lemon juice onto the mackerel fillets and heat under the grill for about 5 minutes. Put on the plates sprinkled with chopped parsley.
• 7
  Add overlapping pickled beetroot slices and a small dish of horseradish cream to each plate, then garnish with chopped cucumber and rocket.