Start by cutting the guanciale, pancetta, or bacon into 1/2-inch strips.

In a large heatproof bowl, whisk the whole eggs and egg yolks together. Stir in the cheese and black pepper until thick and paste-like.

Bring 4 quarts of water to a boil, then add the kosher salt and cook the spaghetti until al dente. Before draining, reserve 1 cup of pasta water, then drain the pasta.

While the pasta cooks, place the guanciale in a large cold nonstick skillet. Turn the heat to medium-high and cook for about 4 to 5 minutes until golden and the fat renders out. If using garlic, add it in the last minute.

Add the hot drained spaghetti to the skillet with the meat and toss well to coat.

Transfer the mixture to the bowl with the egg mixture and immediately pour in 1/2 cup of reserved pasta water, stirring vigorously until creamy.

Spoon the carbonara into warm bowls and serve at once. Top with extra cheese, black pepper, and chopped parsley.

Refrigerate leftovers for up to 1 day in a covered container. Reheat gently in a skillet over low heat with a splash of water.