Boiled water caltrops (zhu lingjiao)

Step 1: Rinse 2 ¼ lb fresh water caltrops in a sink of cold water, rubbing off any mud; take care, the horns are sharp. Throw away any that are cracked open or smell sour.

Step 2: Put them in a large pan with 1 tsp salt and 2 slices fresh ginger, if using, and cover with cold water by 5 cm.

Step 3: Bring to the boil over a high heat, then cover, lower to a steady simmer and cook for 30 minutes, until the shells are a deep purple-black.

Step 4: Fish one out and cut it in half: the flesh should be pure white and floury right through, like a cooked chestnut. Common mistake: draining them too soon; underdone caltrops are waxy and grey in the middle, and they must be fully cooked. Simmer 5–10 minutes more if needed.

Step 5: Drain and leave for a few minutes until cool enough to hold. To eat, crack the middle of the shell with your teeth or a nutcracker and squeeze out the nut, or cut them in half and scoop out the flesh with a teaspoon. Watch little ones with the sharp horns.