Heat oil and butter in a large saute pan over medium heat. Add the onion and pancetta and cook until the onions are translucent and the pancetta is beginning to crisp. Remove from the heat and set aside.

Bring a large pot of salted water to a boil and cook the linguine according to package directions until al dente, about 2 to 3 minutes. Drain pasta in a colander (reserve a small amount of the cooking liquid in a small bowl) and return pasta to the pot. Return the pot to the heat and add the reserved pancetta and onion mixture. Stir over high heat until pasta is coated with the pancetta mixture.

In a bowl, whisk together the egg yolks and heavy cream and add to the pasta, along with the Parmesan. Remove the pot from the heat and toss the pasta until it is well-coated. Season with salt and freshly ground black pepper, to taste. If needed, add a bit of the reserved pasta cooking liquid to help toss the pasta if it is dry. Serve immediately.