Bring a large pot of water to a boil and cook the dry spaghetti until al dente according to package directions.
In a medium bowl, whisk together the liquid egg whites, whole egg, Pecorino Romano, and Parmesan until the mixture is smooth and well combined.
While the pasta cooks, heat a large skillet over medium heat and sauté the pancetta until it is crispy and the fat has rendered.
Reserve approximately 0.25 cup of the starchy pasta water, then drain the spaghetti thoroughly.
Turn off the heat under the skillet and add the hot spaghetti directly to the pancetta, tossing to coat the strands in the rendered fat.
Slowly pour the egg and cheese mixture over the pasta while whisking or tossing constantly to create a silky, thickened sauce without scrambling the eggs.
Add a tablespoon of the reserved pasta water at a time if needed to reach your desired creamy consistency.
Season the dish with black pepper and sea salt, then garnish with freshly chopped parsley before serving immediately.