I made this when I had some left over garlic shrimp and wanted to do a shrimp alfredo over whole wheat pasta. Lacking the ingredients for a proper Alfredo ( and concerned about the fat load in regular Alfredo) I scrounged around my cupboards and refrigerator and used what I had. The result was wonderful! The roux adds the thickening missing by not using heavy cream and the buttermilk adds a delicious and fat-free tang. Unless you slop it on your pasta with a shovel, this comes out to about 95 calories per serving versus 400-500 for traditional Alfredo - what a difference!