Step 1

In a medium bowl, whisk together the eggs, egg yolks, Parmesan, pecorino, pepper and a pinch of salt. Set aside.

Step 2

In a large sauté pan, heat the oil over medium heat. Add the bacon and cook, stirring occasionally, until the fat renders and the edges crisp, 8 to 10 minutes. Add the onion to the pan and raise the heat to medium-high. Cook, stirring occasionally, until the onion is golden brown and soft, 5 to 7 minutes.

Step 3

If the spaghetti won’t lie flat in the skillet, break it in half. Add it to the pan along with 4¾ cups of water and 1 teaspoon of the salt. Cook, uncovered, stirring and tossing the pasta frequently, until it is cooked through but still al dente, 12 to 14 minutes. If the skillet dries out before the pasta is cooked through, add a little water. The pan should stay moist; having a bit of extra pasta water in the pan will make for a creamier, silkier carbonara sauce.

Step 4

Remove the pan from the heat and stir in the egg-cheese mixture, tossing well. Add the spinach, in batches as it begins to wilt, the basil, parsley and remaining 1/2 teaspoon salt and energetically toss until everything is well incorporated. Cover the pan for 2 minutes to allow the spinach to fully cook. Uncover and toss again.

Step 5

Serve immediately, sprinkled with pecorino and pepper.