My favorite way to eat them is to make a quick refrigerator pickle with garlic and white balsamic vinegar. Easy!
Clean well and place fiddleheads in a glass bowl or jar with a few cloves of peeled garlic and a few sprigs of fresh tarragon. Stir together a volume of white balsamic vinegar equal to the volume of fiddleheads, about 1/4 as much water, a teaspoon or two kosher salt, about the same of sugar. Heat until just about boiling. Pour over fiddleheads, cover tightly and refrigerate overnight. They can be eaten the next day, but improve after a more 2-3 days. They are crunchy, and full of flavor in a wild, bright way.
Great with fresh trout (especially when cooked on a stick over a campfire).
Sorry my recipe is so non-specific as far as measurements (I usually hate that!) but I always just throw together refrigerator pickles-it's more a process than a recipe.