Step 1

Bring a large pot of salted water to a boil over high heat.

Step 2

Whisk together the eggs, yolks, Parmesan, Pecorino, pepper and butter if using in a large bowl until well combined.

Step 3

Add the pasta and cook as the label directs. Reserve 1 cup cooking water, then drain the pasta.

Step 4

Meanwhile, cook the pancetta in a large skillet over medium heat, stirring occasionally, until crisp, about 8 minutes. Add the spaghetti and half the reserved pasta cooking water to the skillet and toss to combine.

Step 5

Add the egg mixture and toss to coat. Cook, tossing continuously to avoid scrambling the eggs, until the sauce is creamy, thinning it with the remaining pasta water if it becomes too thick (it should be saucy but not watery), about 1 minute.

Step 6

Divide the pasta among plates and sprinkle with more grated Parmesan.