Heat a large frying pan over medium heat, add the guanciale and cook for about 5 minutes, or until golden brown. If the guanciale is on the lean side, add a splash of olive oil. Transfer to a plate and set aside.
In the same pan with the fat, add garlic and chili flakes and sauté for 1 - 2 minutes over medium heat, until fragrant. Add passata, reduce heat to medium-low and simmer for 10 minutes.
Meanwhile, bring a large pot of salted water to a boil. Add bucatini and cook for 10 minutes, until it’s still firm and about 80% cooked. Drain, then add pasta to sauce and cook for another 5 minutes, or until it’s al dente. Transfer pasta to a serving platter and garnish with pecorino and crispy guanciale. Serve with a rustic red wine and crusty bread.