Prepare the pasta water: Fill a large pot with lightly salted water and bring to a rolling boil. Add a pinch of salt (the water should taste like the sea).

Cook the guanciale: While waiting for the water to boil, heat olive oil in a large skillet over medium heat. Add the diced guanciale and cook until crisp and golden, about 5-7 minutes. The fat should render and become translucent.

Build the sauce base: Add the chopped onion to the rendered fat and cook until soft and translucent, about 3-4 minutes. Add minced garlic and red pepper flakes, sautéing for another 30 seconds until fragrant.

Create the tomato sauce: Pour in the crushed tomatoes, stir well, and season with a pinch of salt and freshly ground black pepper. Reduce heat to medium-low and simmer for 15 minutes, allowing the sauce to thicken slightly.

Cook the bucatini: When the water reaches a rolling boil, add the bucatini pasta and stir gently to prevent sticking. Cook uncovered, stirring occasionally, until the pasta is al dente (tender but still firm to the bite), about 11 minutes or according to package instructions.

Reserve pasta water: Before draining, scoop out about ½ cup of pasta cooking water and set aside.

Drain the pasta: Drain the bucatini but don't rinse it – you want to preserve the starch that helps the sauce adhere to the pasta.

Combine pasta and sauce: Add the drained bucatini directly to the skillet with the sauce. Toss well to coat the pasta evenly, adding a splash of the reserved pasta water if needed to loosen the sauce.

Finish with cheese: Remove from heat and stir in the grated Pecorino Romano cheese until melted and well incorporated.

Serve: Divide the bucatini between two warmed plates. Top with additional Pecorino Romano and fresh basil if desired. Serve immediately while hot.