Cut the pancetta into strips or small dice. Place in a frying pan over medium-low heat on the hob without adding oil. Cook until golden and crisp, then remove with a slotted spoon and set aside, leaving the fat in the pan.
In a large bowl, whisk together the egg yolks and whole egg. Stir in the grated Pecorino Romano and freshly ground black pepper to taste until smooth.
Bring a large saucepan of water to the boil. Add a generous pinch of coarse sea salt and cook the spaghetti al dente according to the packet instructions.
Before draining, reserve about 150 ml of the pasta cooking water. Drain the spaghetti and add it to the pan with the pancetta fat, tossing to coat.
Remove the pan from the heat. Quickly pour in the egg and cheese mixture along with a splash of the reserved cooking water, stirring vigorously to form a silky sauce. Add more cooking water if needed to reach your desired consistency, then stir in the crispy pancetta.
Serve immediately, sprinkled with extra grated Pecorino and an extra grind of black pepper.