I’ve enjoyed cattail often.
Best time to harvest the edible tips is when the upper half (pollen stick) is about exposed from the green sheath in the spring and the lower half is still wrapped in the sheath. Harvest both if you are hungry or the supply of cattails is sparse, harvest only the pollen top if you are picky. Use snippers.
Boil them in lightly salted water for 4 or so minutes until tender, like Asparagus in a large frying pan. They will be soft, almost to where the pollen fibers fall off. Drain and serve.
Add a little butter, maybe sprinkle on spices, and enjoy while they are hot on the stick. The flavor is really nice, on par with good corn on the cob but richer. You can get an appetite for it, and every spring it becomes a craving. The pollen tips are easier to eat, you get more good food for less picking, while the lower parts are a little different flavor, more like spinach than corn. Still very good.
The trick is to catch them on the day the tops are out but the bottom parts are still in the sheath. LIke strawberries or Zuccini, you have to pick them on the day they are ready. It calls for watching the patch you want to pick.
Thanks! I know where there is quite a large group near here in uncontaminated water, and I was planning on trying them this spring.