Here's an oldie from my collection. I use this when I make veggie lasagna, but I am sure it can be used as a pasta sauce. Easy to make. You can make the sauce richer by subbing whole milk, or by using cream or evaporated milk for part of the skim milk. Sometimes I melt a tablespoon of butter and make a roux with the flour before adding my liquid. Very versatile sauce. Note: Prep time does not include time for spinach to defrost.