Recipe: Jerusalem artichoke soup with grilled mackerel

The soup

• 500g Jerusalem artichokes, scrubbed
• 2tbs unroasted sesame oil
• 4 large komatsuna or bok choy leaves, stems removed
• 4 centre pieces of mackerel fillet, skin on, weighing about 30g each
• ¼tsp flaky sea salt
• Neutral oil such as canola, safflower or peanut for deep-frying

To make the clam broth, place the clams in a small saucepan and add 500ml of cold water and the sake. Cover and bring to a lively simmer over medium-high heat. Cook for 3-5 minutes, or until the clams have opened. Scoop out the clams with a wire-mesh skimmer and use them in another dish.

Strain the broth through a piece of paper towel or an unbleached coffee filter to remove sand particles.

Do not peel the Jerusalem artichokes. Cut half of one into 1cm cubes and set aside. Cut the remaining Jerusalem artichokes crosswise into fine slices. Drop the slices into a medium pot, and add the sesame oil and 250ml of the clam broth. Bring to a boil over medium-high heat, then adjust to a lively simmer. Cook for about 20 minutes, until the slices are completely soft.

Purée in batches in the blender until smooth. Pass through a fine sieve back into the clean pot and keep warm on the lowest heat possible (using a flame tamer if you have one).

Fill a medium saucepan with water and bring to a boil. Blanch the komatsuna leaves for 30 seconds (or one minute for bok choy). Drain and refresh under cold running water until cool to the touch. Shake off excess water and pat dry in a clean dish towel. Chop roughly.

Sprinkle both sides of the mackerel with the salt. Place on a rack set over an oven pan and grill for two minutes on each side under a preheated grill, 10cm from the heat.

Heat 5cm of oil in a small heavy saucepan over medium heat. Once hot but not smoking, deep-fry the reserved Jerusalem artichoke cubes for about two minutes, until golden brown and crispy. Drain on paper towels.

Ladle 60ml of the soup into four wide shallow soup bowls and set a grilled piece of mackerel in the middle of each bowl. Garnish with the blanched greens and fried Jerusalem artichoke. Serve steaming hot.