Add diced pancetta to a cold large skillet over medium heat and render for 7 to 9 minutes until crisp. Add sliced garlic and cook 1 more minute, then pull the pan off the heat.

Whisk together eggs, egg yolk, grated Parmesan, grated Pecorino Romano, and cracked black pepper in a bowl until a thick paste forms.

Cook spaghetti in well-salted boiling water for 9 to 11 minutes until al dente. Reserve 1/2 cup pasta water, then drain without rinsing.

Add hot drained spaghetti to the skillet with the pancetta fat and toss over medium-low heat for 1 minute until glossy. Remove from heat.

Pour the egg and cheese mixture over the pasta and toss with tongs, adding reserved pasta water 2 tbsp at a time until the sauce is glossy and coats every strand. Twirl into 4 bowls and finish with extra Parmesan, remaining pancetta, and a crack of black pepper.