Preheat oven to 350°F

Cook spaghetti according to package directions. Set aside.

Lay sliced pancetta flat on a baking sheet and place in oven for approximately 15 minutes or until crispy.Transfer slices to paper towel and set aside.

In a pan over medium heat, sweat onions in butter until translucent, not browned.

Add crushed spinach, parsley and cream to onions; boil mixture over high heat.

Using a hand blender, blend mixture at high speed until smooth. Strain directly into saucepan.

Toss pasta with cream sauce.

Add pancetta, grated Parmesan, egg yolk and olive oil; serve immediately.