Whisk eggs, yolks, finely grated Pecorino, and pepper in a large heatproof bowl.

Place guanciale in a cool skillet and set over medium-low heat. Cook 8 to 10 minutes, stirring, until golden and the fat has rendered. Turn off heat; keep the guanciale and about 3 tablespoons fat.

Cook spaghetti in lightly salted boiling water until al dente. Reserve 1 cup pasta water. Toss drained pasta with guanciale and its fat.

Let the skillet cool off the heat for about 1 minute. Transfer pasta to the egg mixture, tossing constantly. Add hot pasta water 1 tablespoon at a time until the sauce is smooth and glossy.

If the sauce is too thin, set the bowl over the pot of hot water, without touching the water, and toss briefly until it thickens. Serve immediately. Use pasteurized eggs for a lower-risk preparation; this gentle method may not fully cook ordinary eggs.