Preheat your oven to 375°F (190°C) and grease a 9x13 inch baking dish.
Cook spaghetti in well-salted water until just shy of al dente - it'll continue cooking in the oven.
While pasta cooks, crisp the pancetta in a large skillet over medium heat until golden. Remove with a slotted spoon and set aside.
In a large bowl, whisk together eggs, both cheeses, garlic, heavy cream, and black pepper.
Reserve 1/2 cup pasta water before draining the spaghetti. Quickly toss the hot pasta with the egg mixture, adding reserved pasta water as needed to create a smooth sauce.
Fold in the crispy pancetta and transfer everything to the prepared baking dish.
Top with breadcrumbs and a light sprinkle of both cheeses.
Bake for 20-25 minutes until golden brown and bubbly.
Let rest for 5 minutes before serving. Garnish with parsley and extra black pepper.