Your hardest task will be to find crosnes. Large farmers markets will have them in fall and winter, as will specialty markets. Probably easier would be to buy crosnes online. If anyone can located a reliable source for the tubers (for growing), please let me know in the comments section. I like a little drizzle of Oregon White Truffle Oil on this dish, but you could use another truffle oil or just leave it out. I like it because it gives the dish an earthy, luxurious base note underneath the crunch of the crosnes and the brightness of the lemon and parsley.
You can also serve this as a cold side dish, but if you do, use olive oil instead of duck fat don't add the lemon juice until you are ready to serve.