How to Make It
Bring a large pot of water to a boil. In a large, deep skillet, heat the olive oil. Add the leeks and cook over moderate heat, stirring occasionally, until softened and just beginning to brown, about 10 minutes. Add the chicken stock, lemon juice, lemon zest and parsley and bring to a boil. Transfer the mixture to a blender and puree until smooth. Season with salt and pepper.
Meanwhile, add salt to the pot of boiling water. Add the pasta and cook until it's almost al dente. Drain the pasta, reserving 1/2 cup of the cooking water. Return the pasta to the pot.
Add the leek sauce and the reserved cooking water to the pasta and cook over moderate heat, stirring occasionally, until the pasta is al dente and coated with a thick sauce, about 3 minutes. Stir in the 1/2 cup of cheese and season with salt and pepper. Serve immediately, passing additional cheese at the table.