crushed by hand or with a potato masher into rough ½inch chunks One 6-ounce can tuna packed in olive oil, drained (optional) Freshly ground black pepper 1 pound spaghetti 2 tablespoons chopped fresh parsley Grated Parmigiano-Reggiano or Pecorino Romano for serving Bring a large pot of salted water to a boil over high heat Heat the olive oil and butter in a large saucepan over medium-high heat until the butter has melted and the foaming subsides Add the onion and cook, stirring frequently, until softened but not browned, about minutes Add the garlic, anchovies, and pepper flakes and cook, stirring, until the garlic is light golden, about 3 minutes Add the capers, olives, and tomatoes, with their juice, and cook, stirring frequently, until the sauce has reduced and the oil starts separating, about 15 minutes Gently fold the tuna into the sauce, if using, and season to taste with salt and pepper Set aside Cook the pasta in the boiling water until it is fully softened but retains a slight bite in the center (about minute less than the package recommends after the pasta reaches a boil) Drain the pasta, reserving cup of cooking liquid, and return to the pot Add the sauce to the pasta and stir to combine, adding some of the reserved pasta water as necessary to thin the sauce to the desired consistency Serve immediately, topped with the parsley and grated cheese ...topped with the parsley and grated cheese