This recipe is adapted from Marcella Hazan, but there are plenty of variations out there. If you can find guanciale – pork jowl – use that instead of pancetta. Onions are optional in some recipes, while others add garlic and a splash of white wine. Some call for olive oil or lard. You can use spaghetti, or try bucatini or perciatelli – thicker spaghetti with a hole through the middle. The latter can be tricky to cook because it goes from not-quite-done to too-soft quickly. Try this: When it is nearly done (very al dente), add to the sauce along with a spoonful of pasta cooking water, then stir and cook over heat for a minute or two to finish cooking. Add cheese and stir again and serve immediately. 

In a large saucepan over medium heat, combine butter and oil. Add onions and cook until they just start to take on color. Add pancetta and fry for two minutes. Add tomatoes, hot pepper and salt and cook over medium-low heat about 25 minutes, or until you can see the fat on the top. Turn off heat.

Meanwhile, bring large pot of water to boil. Add salt and pasta. Return to the boil and cook about 10 minutes until very al dente. Drain and add to sauce. Stir over heat for a minute or two to finish cooking. Stir in grated cheese and serve immediately. Serves 4.