In a large skillet, heat the olive oil over medium heat. Add the pancetta and cook until browned and the fat is rendered, about 5 minutes. Use a slotted spoon to transfer to a paper towel-lined plate.
Add the onions to the skillet and saute until translucent, 7 to 8 minutes. Stir in the garlic and a pinch of crushed red pepper (a generous pinch if you like spicy). Cook, stirring, about 2 minutes. Add the tomatoes and use a wooden spoon to break up any large pieces. Add the pancetta back to the skillet. Add salt and a pinch of crushed red pepper. Bring to a low simmer, cover and cook until the flavors have melded and the sauce is slightly thickened, 20 to 30 minutes.
While the sauce cooks, bring a large pot of water to a boil. Season generously with salt. Cook the pasta according to the package directions. Stir 1/2 cup of the pasta water into the sauce (skip this step if using gluten-free pasta), then drain the pasta. Add the pasta and cheese to the sauce and toss to coat. Serve with additional cheese.
This recipe has been updated and may differ from what was originally published or broadcast.