I heat the skillet over medium heat and add the diced pancetta. As it cooks, I let it render its fat and crisp up, stirring occasionally. When golden and crunchy, I stir in the coarse black pepper so the fat picks up that spiciness.
While the pancetta is cooking, I bring a large pot of salted water to a boil (using the 1 teaspoon kosher salt). I drop in the gnocchi and cook until they float, usually 2–3 minutes if fresh (slightly longer if frozen). Using a slotted spoon, I lift them out and reserve some of the starchy water.
I add the gnocchi into the hot skillet with pancetta and toss, coating them in the rendered fat. I pour in about ⅓ cup of the reserved cooking water to help loosen things up, stirring gently to combine.
In a separate bowl, I whisk together the egg, yolk, grated Pecorino, and Parmesan until smooth and well blended. The mixture should be thick. If needed, I add a bit of reserved water to adjust consistency.
Off the heat, I slowly stream the egg-cheese mixture into the skillet while stirring constantly—so the sauce becomes silky, not scrambled. If things get too thick, I return to very low heat briefly, adding more water a tablespoon at a time until smooth.