Prep the sauce base. In a bowl, whisk the eggs and extra yolk with Parmesan and Pecorino until smooth. Add a generous pinch of black pepper. Set aside.

Cook the pasta. Bring a large pot of salted water to a boil. Cook spaghetti until just shy of al dente. Dip out 1–1.5 cups of pasta water before draining.

Crisp the bacon. While the pasta cooks, sauté the bacon in a large skillet over medium heat until golden and crisp. If using garlic, stir it in for the last 30 seconds. Turn off the heat. Spoon off excess fat if there’s more than a couple of tablespoons, but keep enough to coat the pasta.

Combine pasta and bacon. Add the drained spaghetti to the skillet with the bacon. Toss to coat in the rendered fat. If the skillet is very hot, let it cool for a minute to prevent scrambling the eggs.

Create the sauce. Pour the egg-and-cheese mixture over the pasta, tossing quickly. Add a splash of hot pasta water and keep tossing until the sauce turns glossy and creamy. Add more water as needed to loosen and emulsify.

Season and finish. Taste and adjust with black pepper. Add a pinch of salt only if needed—the cheeses and bacon are already salty. Top with extra cheese and a little parsley if you like.

Serve immediately. Carbonara is best hot and fresh, while the sauce is silky.