In a large pot of boiling salted water, cook the spaghetti until just al dente. Drain, reserving 1/2 cup of the pasta cooking water*.
Meanwhile, in a small bowl, whisk the egg yolks and cream.
In a large, deep skillet, heat the oil. Add the diced pancetta and cook over moderately high heat, stirring, until crisp, 4 minutes.
Add the garlic and cook until golden, 1 minute.
Add the spaghetti to the skillet. Cook over low heat, tossing, until coated.
Slowly add the reserved pasta cooking water and beaten egg yolks. Toss until coated with a creamy sauce, about 1 minute.
Add the 1 cup of Parmesan and the nutmeg; season with pepper.
Transfer to bowls and serve, sprinkling with the extra Parmesan.