I know what the recipe is supposed to accomplish, but it just doesn't do it. When prepared as written, it'll take you forever to get the sauce to thicken and you'll end up losing so much of the sauce that you'll wonder why you bothered. And the sauce is just too bland. I spent as long trying to fix the recipe as I did making it.
My basic suggestions are to replace the oil you saute the garlic and onions with "I can't believe it isn't butter". It makes a difference. Secondly, when making the sauce, first add 3 TBL of the butter substitute with the 3 TBL of flour, and heat and whisk it until the butter melts and the flour breaks up. THEN add the milk and the stock, s&p, whisking constantly as you bring the liquid to a boil. By the time it boils, the sauce will have thickened quite well (actually you might need to thin it a bit with more milk and stock) and you'll have made a basic white sauce. Then, add a dash of powdered mustard, red pepper, and garlic (the garlic flavor needs to steep into the mixture a bit better and more "Alfredo" like). I added basic Italian seasonings for fun. And I think I doubled the amount of Parm. cheese.
I think most people will be far more pleased with the resulting sauce and it sure is a lot faster to make. Plus, since the sauce you make is a basic white sauce, you can add what you want without messing it up.