In a large pot of salted boiling water cook the spaghetti according to the package directions. Reserve ½ cup pasta water and drain well.

While the pasta is cooking, whisk the eggs and egg yolk together in a small bowl. Add the Pecorino and Parmesan cheese to the eggs, whisk and set aside.

Place diced pork belly (or bacon) into a cold large skillet and then turn the heat to medium-high. Let the fat render out, stirring occasionally.

After about 6 minutes, add sliced mushrooms, finely diced serrano, and roasted garlic paste to the pan with the pork belly. If there isn’t enough oil in the pan, add some extra reserved bacon fat or butter. Season the mixture with the black pepper, salt, crushed red pepper, and dried oregano. Cook for an additional 2 minutes.

Turn off the heat and remove the pan from the burner. Add in the cooked spaghetti. Also, add in a ¼ cup of the reserved pasta water. Add the egg mixture to the pan and gently toss to combine. Add more reserved pasta water a tablespoon at a time until the sauce is to your desired consistency. Continue tossing until the pasta is coated nicely.

Serve immediately and garnish with Parmesan cheese and parsley, if desired.