How to Make It
Cook pancetta in a large skillet over medium, stirring occasionally, until lightly browned, about 4 minutes. Add shiitakes and garlic; cook, stirring often, until tender, about 6 minutes. Set aside.
Cook spaghetti according to package directions; reserving 3 tablespoons cooking liquid. Meanwhile, whisk together pecorino Romano, egg yolks, and egg in a large serving bowl.
Add hot spaghetti and reserved cooking liquid; toss until cheese is melted and yolks thicken. Stir in shiitake mixture; garnish with parsley.
Note: The heat from the pasta cooks the eggs, but not thoroughly. It may be advisable for young children, the elderly, and anyone with a compromised immune system to avoid eating this dish.