I found this recipe at one of my favorite recipe blogs Our Best Bites. My pickiest eaters asked for seconds on their pasta and loved the sauce. I double the recipe so I could freeze the leftovers. Here is the original recipes because as always, I made some changes.
1 1/4 C skim milk
1/4 c half & half
1/3 C (3 oz) 1/3-less-fat cream cheese
2 T flour
1 t salt
1 T light butter
3 garlic cloves, chopped finely
1 C finely grated Parmesan cheese
Toss the milk, cream cheese, flour, and salt in a blender. Process until smooth and set aside. In a non-stick pan, melt butter on med-high heat and add garlic. Let the garlic saute for about 30 seconds. Then add milk mixture to the pan. Stir constantly for about 3 or 4 minutes or until it just comes to a simmer. Keep stirring and let it cook for a few minutes more. It should be much thicker now.
When it's thick (it should look as thick as a normal alfredo sauce) remove the pan from the heat. Add the cheese, stir it up and then cover immediately. Let stand for at least 10 minutes before using. It will continue to thicken upon standing.
Freeze leftovers. When ready to use thaw in the fridge. Just re-heat and add a little milk and it will be back to normal again.