"Sea urchin is in its best condition when the water is cooler," says Moyle. "The water temperature in Tasmania can rarely be accused of even bordering on comfortable, but the autumn-winter months are when urchins take full advantage of the cold currents. The quality of the urchin in this dish is of the utmost importance - they can go from being the best thing you could possibly eat to the contrary in a heartbeat."
Note Katsuobushi, dried, fermented and smoked skipjack tuna, is available from Japanese grocers. If it's unavailable, substitute bonito. To prepare sea urchin, either snip carefully around the tip, as if taking the top off a boiled egg, or chop it down the middle to open. Remove the five fingers or lobes of roe, wash briefly in cold salt water and remove the thin black membrane covering each lobe. You can also buy sea urchin cleaned from fishmongers. You may need to order it ahead.