Heat oil in a large heavy, wide skillet over medium heat. Add guanciale or pancetta and sauté until beginning to crisp and color, about 4 minutes. Add pepper flakes and a generous amount of black pepper; stir for 10 seconds. Turn heat up to medium-high. Add wine, scraping up any browned bits on the bottom of the pan, and continue to cook for a few minutes, stirring often, or until the wine has almost all evaporated but the mixture still looks a bit juicy.

Add tomatoes, reduce heat, and simmer until sauce has thickened, stirring occasionally. This will take about 15 or 20 minutes - the time it will take you to cook the spaghetti itself.

Bring a large pot of salted water to a boil. Add spaghetti and cook, stirring now and then, until it is firmer than al dente. It is very important not to completely cook at this point. Drain pasta, reserving 1 cup of pasta cooking water.

Add drained pasta to sauce in skillet over low-medium heat and use tongs to toss and thoroughly coat with sauce. Add reserved water, a few tablespoons at a time, and keep tossing until sauce comes together with pasta is coated evenly and well. Toss in cheese and serve immediately, with extra cheese passed around.