Wow, this is good! It's not the most high-protein thing in the world, but it's creamy and rich and satisfying, and you can sprinkle toasted almonds on top if you like.
I made this without the nutritional yeast. It was incredibly yummy. I used a bag of frozen spinach, and I think if I did it again I would try two.
Also: this looks like a good recipe blog!
Creamy Spinach Pasta Sauce