Cook the pasta: Bring a large pot of salted water to a boil. Add the pasta and cook 1 minute less than package instructions for al dente. Reserve 1 cup of the pasta cooking water then drain the pasta.
Meanwhile, prepare the sauce: Transfer the anchovies from their tin to a cutting board but reserve the oil in the tin. Roughly chop the anchovies. Heat the reserved oil (if using) plus the olive oil in a large skillet over medium-low heat. (If you’re using the oil from the tin, use 2 tablespoons of olive oil. If you’re not, use 3 tablespoons of olive oil.) Add the anchovies, garlic, and red pepper flakes and cook until the anchovies dissolve and the garlic just begins to turn pale golden brown, 2 to 3 minutes. Remove the skillet from heat if the pasta isn’t ready yet.
Toss the pasta: Add the reserved cup of pasta water to the pan and bring to a simmer over medium-high heat. Simmer until the liquid is reduced by about half, 4 to 5 minutes. Add the pasta and toss continuously until the sauce is thick and glossy and the pasta is al dente, 1 to 2 minutes more. Remove from the heat and stir in the parsley, if using, and toss to combine. Serve garnished with grated Parmesan and, if desired, more red pepper flakes. Love the recipe? Leave us stars and a comment below!
