1 1/2 cups thinly sliced white mushrooms (5 ounces)
Salt and freshly ground black pepper
1 small head escarole (about 1/2 pound), cored and cut into 1-inch ribbons
6 tablespoons freshly grated Parmesan cheese, plus more for serving
In a large pot of boiling salted water, cook the fettuccine until just al dente. Drain the fettuccine, reserving 1 cup of the cooking water.
In a large, deep skillet, heat the olive oil until shimmering. Add the garlic and crushed red pepper and cook over moderately high heat until fragrant but not browned, about 30 seconds. Add the mushrooms, season with salt and pepper and cook until softened and just beginning to brown, about 5 minutes.
Add the escarole to the skillet and cook, stirring, until wilted. Add the fettuccine and the reserved cooking water and cook, tossing gently, until the sauce is slightly thickened, about 2 minutes. Season the fettuccine with salt and pepper. Add the 6 tablespoons of Parmesan cheese and toss to coat. Transfer the pasta to plates or bowls and pass extra Parmesan at the table.