Any pasta will work with this sauce. You can also use kale but it will need to blanched by immersing it in the boiling pasta water for 5 minutes. Kale should be bright green and tender but not mushy or overcooked.
This sauce does not keep. Spinach darkens and changes flavor after it cools. If not using all of the sauce at once, set aside 1/2 of the base and the spinach. Store separately. When ready to use the remainder of the sauce, reheat and blend with fresh spinach.
Find it online: http://shiftycrafty.com/penne-spinach-cream-sauce/