Please review these important food safety notes from Health Canada: https://www.canada.ca/en/health-canada/services/food-safety-fruits-vegetables/fiddlehead-safety-tips.html
Using your fingers, remove as much of the brown papery husk on the fiddlehead as possible.
Wash the fiddleheads in several changes of fresh, cold water to remove any residual husk or dirt.
Cook fiddleheads in a generous amount of boiling water for 15 minutes, or steam them for 10 to 12 minutes until tender. Discard the water used for boiling or steaming the fiddleheads.
Cook fiddleheads before sautéing, frying, baking, or using them other foods like mousses and soups.
Clean the fiddleheads properly.
Boil them for two minutes.
Discard the cooking water.
Plunge the fiddleheads into cold water and drain.
Pack the fiddleheads in freezer containers or bags.
Store fiddleheads in the freezer for up to one year for best quality.
Follow the complete cooking instructions above before serving.
Never re-freeze thawed food.