Typically it is done with spaghetti, but on my last trip to Rome in 2009, I found rigatoni alla carbonara. Equally good, and probably a bit easier to eat.
1 lb spaghetti or spaghettini
6 slices thick-cut bacon, or 8 slices regular bacon, cut up into 1/4-inch pieces
1/2 tsp salt
Cook the spaghetti to al dente in liberally salted boiling water.
While the pasta is cooking, sauté the bacon over medium heat until cooked, but not crisp. Set aside with the rendered bacon fat.
Beat eggs well in a bowl. Add 1/2 teaspoon salt.
Black pepper and beaten eggs.
When the pasta is cooked, reserve a cup of the pasta cooking water. Drain the pasta and dump into serving bowl. Add beaten eggs, about half the cooking water, and the bacon with reserved fat to the pasta, and mix very well, until all the strands are coated with a creamy, eggy sauce. Sprinkle liberally with black pepper.
The composed dish.
Though the Romans would not likely do it, I'm not averse to adding a tablespoon or two of butter to the hot pasta.
Serve immediately. Pass grated cheese at the table.
Rigatoni alla carbonara, at a small trattoria in Rome.