Dice the guanciale and place it in a cold skillet. Heat over medium-low flame for about 10-15 minutes until golden-brown and crispy.

If desired, remove guanciale from skillet and add minced garlic to the rendered fat, sautéing for 1-2 minutes until fragrant.

In a mixing bowl, whisk together the eggs, grated Pecorino Romano cheese, grated Parmesan, and black pepper until smooth.

Boil salted water in a large pot and cook spaghetti according to package instructions until al dente, about 8-10 minutes. Reserve 1 cup of pasta water before draining.

Return spaghetti to the warm skillet with guanciale fat. Toss for a minute to coat the pasta.

Remove skillet from heat, pour in the egg mixture, and quickly toss the pasta until evenly coated.

Stir in crispy guanciale and adjust sauce consistency with reserved pasta water as needed. Serve immediately with extra Pecorino Romano.