Kuwai no nimono (simmered arrowhead)

Step 1: Soak ⅓ oz kombu (dried kelp) in 2 cups water for at least 30 minutes (this can be done the day before, in the fridge). Remove the kombu just before the water would boil when you heat it later.

Step 2: Trim the sprout of each 12 kuwai (arrowhead tubers) to about 4 cm at an angle and cut the bottom flat so it stands up. Peel the sides in six even strokes from base to top, so each tuber looks hexagonal like a turtle shell, and drop them into cold water.

Step 3: Put the kuwai in a pan of cold water with 1 tbsp raw rice, bring to the boil over medium heat and simmer for 5 minutes to draw out the bitterness. Drain and rinse gently.

Step 4: Heat the kombu dashi in a small pan, remove the kombu as it reaches a simmer, then stir in 2 tbsp sugar, 2 tbsp mirin, 1 tbsp light soy sauce (usukuchi) and ½ tsp salt.

Step 5: Add the kuwai standing in one layer, cover with a drop lid or baking paper and simmer on the lowest heat for 15–18 minutes, until a skewer slides into the centre easily. Common mistake: a rolling boil, which makes the tubers crack and the sprouts break off.

Step 6: Leave the kuwai to cool completely in the liquid, ideally overnight in the fridge, so they turn evenly pale gold. Serve at room temperature with a little of the liquid; they keep 3–4 days chilled. For the classic version, use bonito (katsuobushi) dashi instead of kombu dashi.