This recipe makes 2 pints and can be scaled up or down, and you will notice not everything is exact; pickling is like that because one fiddlehead might be twice as large as another. Also, I like these seasonings with the fiddleheads, but feel free to use your own. The only thing you shouldn't mess with is the salt-to-water ratio. This protects the vegetables from bad bacteria.
Trim the browned ends off each fiddlehead. Discard any that are mushy or crushed. Bring a large pot of water to a boil and salt it well. Boil the cleaned fiddleheads for 2 minutes, then plunge them into a bowl of ice water.
Dissolve the 1/4 cup of salt in the quart of water. Fill a glass jar (I use a Mason quart jar) 3/4 of the way up with fiddleheads, which should be the whole pound. If not, use more jars and brine. Cover the fiddleheads with the brine by about an inch. Weigh them down. I use a narrow jelly jar set into the larger wide-mouth Mason jar, but a plastic bag filled with brine works well, as might a clean rock.
Keep the jars in a cool, darkish place away from direct sunlight, which can rob the fiddleheads of their color. Let them ferment for at least a week, and up to 2 weeks. You might notice a little mold on the top of the brine: This is perfectly OK, just skim it off.
When the fiddleheads taste crunchy and tangy, which I noticed after about 10 days, you are ready to store them. I fill pint jars with the spices -- split 50-50 -- and then repack them with fiddleheads. Pour over the brine from the original jars and screw on lids. Keep in the fridge indefinitely, although they will get tangier as time goes by.
Fermentation time is up to you. The pickles should be ready after about 5 days, but they will get tangier as time passes. I put mine in the fridge after two weeks, which gave them a sourness like a kosher dill pickle. Once the pickles are in the refrigerator, they will continue to ferment, but very slowly. I've held similar pickles for a year and they were still good.