This is a very important dish in Italian cuisine. It gives you a taste of pork from the guanciale, a shot of salt from the pecorino, and a touch of acid from the tomato. It is the quintessential example of a perfect combination that should never be altered.
Bring a large pot of salted water to a boil over high heat. Drop in the pasta, quickly return to a boil, and cook until tender yet firm, 2-7 minutes, depending on how long it has been refrigerated (or 8-9 minutes for the dried stuff). Drain the pasta, reserving the pasta water.
Meanwhile, heat 4 teaspoons of the oil in a large sauté pan over medium-high heat. Add the guanciale and cook until crispy and golden brown, stirring now and then, about 5 minutes. Add the tomatoes and pepper flakes and break up with tongs. Add the wine and 2 cups pasta water and boil until the sauce reduces in volume and thickens slightly, about 10 minutes.
Add the drained bucatini to the pan along with 1 cup of the pecorino, parsley, and remaining olive oil. Season with salt and pepper, to taste, tossing until the sauce is creamy. If the sauce gets too thick, add more pasta water. Divide among warm pasta bowls and garnish with the remaining 1 cup pecorino.