Start by blanching the fiddleheads in a pot of boiling salted water. Cook for about 5 minutes, drain and cool in ice water bath. Drain and set aside.
Garlic should be sliced very thinly. A mandolin is perfect for this job.
Cut pancetta into thin strips.
Cook linguini in boiling salted water till 'al dente'. Drain and mix with 1/4 cup olive oil.
Slowly heat olive oil in a shallow pan, add garlic slices and cook until browned. Careful because too much heat will just burn them. Add some lemon juice to stop the cooking.
Reheat the fiddleheads in a pan with a small amount of olive oil or butter and add to the linguini.
Add olive oil, garlic and lemon juice to the hot pasta as well as the pancetta and chopped parsley. Finally add the fiddleheads.
Mix and serve. Top with cracked black pepper and grated parmesan.
Fiddleheads are available in the early spring here in the Northeast and the season is just a few weeks long. If you can't get them, I suggest using asparagus as a good substitute. Enjoy.