1 to 1 1/2 cups fresh shelled fava beans
2 tbsp. EVOO
2 medium leeks, trimmed and halved lengthwise, then thinly sliced crosswise, or 1 bunch spring onions, whites and light greens, thinly sliced
4 cloves garlic, chopped
½ cup white wine
1 cup (packed) fresh mint and parsley combined, finely chopped
½ cup (loosely packed)
1 lemon, zested and juiced
1 lb. tagliatelle
3 tbsp. butter
1 cup Pecorino Romano, Parmigiano-Reggiano, or a combination of both
Bring a medium pot of salted water to a boil for the favas and a large pot of water to a boil for the pasta. Prepare an ice bath for the favas.
Add the favas to the medium pot of boiling water. Boil for 5 minutes, then drain, reserving 1/2 cup of the cooking water. Transfer the favas to the ice bath. Drain and peel the favas. In a food processor or blender, puree half of the favas with the reserved water.
Heat a large skillet over medium. Add the EVOO, two turns of the pan. Add the leeks and garlic and cook, stirring often, 2 to 3 minutes. Add the wine; bring to a simmer and cook, 1 to 2 minutes, until slightly reduced. Stir in the fava puree, the remaining whole favas, the chopped herbs, and the lemon zest. Season the sauce with salt and pepper.
Salt the large pot of boiling water, add the pasta, and cook 1 minute less than the package directions. Reserve about 1/2 cup of the pasta cooking water, then drain the pasta. Stir the pasta water into the sauce, then add the pasta, lemon juice, butter, and cheese. Toss until coated.
Serve the pasta in shallow bowls.