Here is a method for preserving fiddleheads that will allow you to enjoy them any time of year just as if they were freshly picked.
I wrote about foraging fiddleheads (the young sprouts of the ostrich fern) in a post last year. Fortunately, this is another great year for them and I was able to pick even more than usual. It is one of those seasonal treats you generally enjoy fresh. Only if you have gathered way more than you can consume immediately do you worry about how to preserve them. Freezing is not really an option as it changes the texture too much. I have not tried pickling or fermenting them as I expect again the texture might not be so appetizing. So I resorted to dehydrating them, and with great success.
First, they have to be cooked, boiled in water for about ten minutes, otherwise they are not easy to digest. After boiling and draining them, use all you can as is, in a stir fry, omelette or whatever. Any excess, dehydrate at 125 degrees F (52 C) for about three hours. They will look diminished and wizened and be very crisp. Store them in a cool dark place in a sealed container. To use for cooking, simply rehydrate them with hot water. In about two minutes they will regain their size, texture, colour and flavour. Even the tiny stems! Drain them and use them as you would fresh ones.
In the aforementioned post of last year, I used fresh ones to make fried pakoras. This year I tried baking instead of frying them. Preparing them in the same way to cook, then placing the coated fiddleheads on a parchment lined cookie sheet and baking them in a hot oven (500 degrees F) for ten minutes gives a softer, less crisp pakora. Either way, they are delicious.