Cut the pancetta (or bacon) into small cubes. Heat olive oil in a pan, and saute the pancetta slowly over medium heat.
When the pancetta is crispy, add the sliced onion and stir fry for 30 seconds or so.
Add white wine, turn the heat up to high, allowing the liquid in the pan to evaporate quickly.
When most of the liquid has evaporated and the contents of the pan look like they did before the wine was added, the crispy pancetta has absorbed all the goodness of the wine.
You can leave the pan for steps 3 and 4, so grate the cheese in the meantime (see Helpful Hints below).
Add tomato sauce to the pan and heat through. Add grated cheese.
When the cheese has melted and blended, mix the sauce with al dente spaghetti and it's done.
Taste and adjust the seasoning after mixing the sauce and pasta together. The saltiness of the ingredients should be enough, though.
Story Behind this Recipe
This pasta is eaten a lot in the Lazio region of Italy, where Rome is located. The tomato sauce with cheese mixes well with pasta. It's easy but it's not that well known, so I've uploaded the recipe.
In Italy we use a type of long pasta with a hole in it called bucatini, but since it's hard to find in Japan, I use thick spaghetti (with a cooking time of about 10 minutes) instead. The authentic version of this recipe uses sheep cheese (Pecorino Romano), but you can use any other natural melting cheese instead.