Cook the Spaghetti: Bring a large pot of salted water to a boil and cook the spaghetti until al dente, as per package instructions. Reserve about ½ cup of the pasta cooking water, then drain the spaghetti.

Prepare the Sauce: In a mixing bowl, whisk together the egg yolks, whole egg, and grated Parmesan until smooth.

Cook the Bacon: In a large skillet or frying pan, cook the diced bacon over medium heat until crispy and golden. If using garlic, add it to the pan during the last minute of cooking, stirring to prevent burning.

Combine and Toss: Immediately transfer the hot, drained spaghetti to the skillet with the bacon. Slowly pour the egg and Parmesan mixture over the hot pasta, tossing quickly to create a creamy sauce. Use a splash of the reserved pasta water if needed to loosen the sauce and ensure it coats the spaghetti evenly.

Garnish and Serve: Season with additional salt and pepper to taste, if necessary. Serve immediately.