Crisp the guanciale in a pan over medium heat until golden and fatty.

Add chili flakes to the pan.

Crush the San Marzano tomatoes by hand and add them to the pan; simmer for 10-15 minutes.

Meanwhile, boil the bucatini in salted water until al dente according to package directions.

Drain the pasta, reserving a splash of pasta water, and toss it into the sauce.

Turn off the heat and mix in the grated Pecorino Romano and black pepper, adding the reserved pasta water if needed to emulsify.