To start, make sure the fiddleheads are thoroughly cleaned and stems are trimmed. Prepare an ice bath (water and ice mixed together in medium bowl). Place a small saucepan full of water, over high heat. When the water reaches a simmer, add the fiddleheads and blanch them for 3 to 4 minutes. This will remove a lot of their bitterness--essential! Drain the fiddleheads and immediately transfer them to the ice bath so they stop cooking. When they're cooled, drain the fiddleheads and dry them thoroughly.
Bring a large pot of salted water to a boil. Cook your pasta until al dente, about 7-9 minutes. Drain and set aside.
In a medium saute pan, set over moderately high heat, add the olive oil and butter. When the butter is melted and the oil is hot, add the fiddleheads, salt and red pepper flakes; cook for 2 to three minutes, tossing every so often. Add the lemon zest, lemon juice, heavy cream and Parmesan-Reggiano. Mix until combined. Add the warm pasta and toss until the noodles are completely dressed. Divide between bowls and top with more Parmesan cheese and a sprinkling of freshly ground pepper.