Cook spaghetti according to packet directions until "al dente". Drain, reserving about 1 ladle of cooking liquid.
Heat a frying pan over medium heat; add guanciale (or pancetta). Cook until nearly crisp, then pour in wine and let the alcohol evaporate. Use a slotted spoon to remove the guanciale; set aside.
In the same pan; add crushed tomatoes, salt and chilli flakes. Simmer for 8 to 10 minutes over low heat, checking often. Stir in the cooked guanciale and remove pan from heat. Stir in cooked pasta, adding some of the reserved cooking liquid if needed.
Sprinkle with pecorino romano cheese, add more chili peppers if like, and serve immediately.
Portion into 4 warm bowls or one large dish, with freshly grated Pecorino and additional chilli flakes on top.