Put a large pot of water on to boil. If the pancetta isn’t chopped already, remove any rind and chop into small cubes about 1/4-inch across. Beat the eggs in a medium bowl. Add the two cheeses to the eggs, season with lots of freshly grated black pepper, and stir to combine. Set aside.

Salt the pasta water liberally. When the water has boiled, add the spaghetti and stir so that the noodles don’t stick together. Cook for about 10 minutes, or until done.

While the pasta is cooking, start the pancetta. Melt the butter in a large skillet over medium heat, and add the pancetta and garlic. Cook on medium heat for about 5 minutes, stirring often, until the pancetta is golden and crisp. You can now discard the garlic, or, if you’re like me and enjoy eating large garlic cloves drenched in butter, feel free to leave them in. (I sometimes chop the garlic coarsely, and then just leave the pieces in. The butter really mellows their flavor, and they become quite flavorful)

After the pancetta has browned, turn the heat to low. Drain the pasta when it’s cooked, but reserve 1 cup or so of the pasta water. Add the pasta to the pancetta in the skillet. Alternatively, you can transfer the pasta straight from the pot to the skillet with a pasta fork or tongs. Either way, don’t worry if pasta water drops in the pan as well (you want this to happen).

Remove the skillet of spaghetti and pancetta from the heat. Pour in the egg and cheese mixture, and, moving quickly, use tongs or a long fork to toss the spaghetti and pancetta with the egg mixture. You’ll want to move and toss the pasta around quickly so that the egg mixture doesn’t cook and scramble. Add some splashes of the pasta water to thin out the cheese sauce to your desired consistency. I would start with about 1/4 cup and add more if needed – I usually end up using about 1/2 cup. The pasta should look silky, smooth, and glossy, and the noodles should slide about fairly freely. If the dish looks dry and stiff, just add more pasta water and mix. Season with a little salt, if needed, and lots of freshly grated black pepper. Toss until everything is combined.

Serve immediately (in warmed bowls, if you're being fancy; spaghetti carbonara cools quite rapidly), topped with more freshly grated black pepper and grated cheese, if you prefer.