A basic way to precook fiddleheads for using in salads, sauteeing, pickling, and general use as a cooked vegetable.
Fiddlehead fernscleaned and trimmed, an inch or two of stem remaining
Bring some water to a boil in a large pot, add the salt until the water tastes "like the sea" (roughly 1-2 tablespoons per quart). Make sure there is at least twice as much boiling water as there is fiddleheads.
While it might be tempting, don't omit the salt. Salt seasons the vegeatables and makes them taste better, but it also extends their shelf life in the fridge, just in case you forget about them for a day or two.
Add the fiddleheads and cook until tender, about 2 minutes. If you want your fiddleheads more well done you can cook them a little longer, but if you cook them too long, they will get mushy. In your kitchen you make the rules, so make sure they taste good to you.
Remove the fiddles and drain, then allow to cool naturally, there is no need to shock them in ice water to keep their color-if you do, they could oxidize and turn dark.
Blot the fiddles with a paper towel to remove any excess moisture, then store in a sealed container or bag in the fridge until you need them. From here they can be cooked as you would any other vegetable, or seasoned and eaten in a salad, etc. They will last for 3-4 days in the fridge.