Fill a large pasta pot ⅔ full with hot water. Add in 2 teaspoons of salt, cover the pot, and heat on high on your stove.
(See the notes if you are using bacon instead of pancetta.)
Peel and chop the entire shallot. In a 12-inch skillet, add the butter and olive oil and heat the pan on medium-high to melt the butter.
Add the shallots and cubed pancetta to the pan and lower the heat to medium. Stir the shallots and pancetta to coat them with the butter and oil, then let them cook for about six minutes, stirring occasionally, until the shallots are soft and the pancetta has started to brown. Turn off the heat.
When the water on the stove is boiling, add the pasta, stir it in, and lower the heat to medium-high. Leave the pot uncovered and stir it occasionally to prevent sticking. After a few minutes, scoop out a couple of ladles of pasta water into a bowl to use for later.
Grate the Parmesan and Romano if needed. (I use my blender.) In a small mixing bowl, crack the eggs and use a whisk to beat them. Whisk in the black pepper, then the grated Parmesan and Romano.
When the pasta seems like it needs another minute to be al dente, turn off the heat and drain the pasta in a colander in the sink.
Transfer the drained pasta to the pan of shallots and pancetta on the stove and stir and toss to combine. Turn the heat on low, then add the egg mixture and half a ladle (¼ cup) of reserved cooking water. Continue stirring and tossing the pasta to allow the egg mixture to come to a safe temperature. When the eggs start to thicken (after a couple of minutes or so), turn off the heat.
Serve immediately, with extra Parmesan if desired. If the pasta seems dry, you can add more reserved pasta water.
If there are leftovers, stir in extra pasta water to them and store the fettuccine carbonara in the refrigerator for up to four days. Add a little butter or olive oil to each serving when reheating in the microwave.
Notes
Shallots look like small, brown onions. When you peel one, you will usually find two purplish bulbs inside. Use both of them.
I buy Citterio cubed pancetta at the grocery store in the refrigerated section near the deli. If you can't find it, buy pancetta at the deli and dice it yourself.
Using Bacon Inestead of Pancetta
When you're starting the recipe, make the bacon first. I don't care for bacon grease in my food, so I recommend cooking the bacon in the microwave instead of a pan.
Line a dinner plate with two paper towels. Place six strips of bacon on the paper towels and cover them with another paper towel.
Microwave the bacon for a couple of minutes, or until it is cooked through but not crispy. Dab the bacon with the top paper towel to absorb the grease. Cut the bacon into pieces with kitchen scissors or a knife.
Proceed to make the shallots and pasta as directed. Add the bacon pieces to the fettuccine carbonara when you stir in the egg mixture.