Storage: Store fiddleheads in a plastic bag in your refrigerator or blanch and freeze for long term storage (
How to Freeze Better at Home).
Shelf Life: Up to two days fresh, several months frozen.

Whether they’re served hot or cold, fiddleheads need to be cooked before consumption. Before cooking, rub off any brown scales and trim to about 1 inch below the coil of the head. Discard any fiddlehead ferns with black scales, slightly purple fiddleheads are safe to eat.
To prepare fiddleheads for cold dishes (like salads), quick cooking dishes where they may not cook through, or freezing, blanch them. How to Prep Fiddleheads
For use in hot dishes, fiddle head ferns can be sautéed, stir-fried, deep fried, or steamed. They should be cooked until they reach an asparagus-like texture with a light crunch that gives when bitten into.
Fiddlehead ferns pair extremely well with wild morel mushrooms, freshly grated nutmeg, bacon, onions/shallots/leeks, salmon fillets, lemon and heirloom potatoes. For a quick and easy condiment, stir some freshly squeezed lemon juice into mayonnaise.
Fiddlehead Fern Recipes