liquid such as broth, milk, or cream
fat or butter
all purpose flour
In general, these are the ratios. Obviously you can make adjustments for the way you want it.
For thin gravies and sauces the ratio is 1 T. fat to 1 T. flour to 1 cup of liquid. For a thicker gravy 1 1/2 T. Fat to 1 1/2 T. Flour to 1 cup liquid.
For “cream of” style thick soups the ratio is 2 T. Fat to 2 T. Flour to 1 cup liquid.
Put your fat in a saucepan on low. Once it has melted, add your flour and whisk together. Cook for 3 minutes.
Add liquid, a little at a time, whisking constantly. Once it is smooth, cook until desired consistency, whisking occasionally. Season to taste.
For Alfredo:
Make sauce with cream (or milk if you need to) as the liquid. Add garlic powder to taste or a bulb of roasted, smashed garlic, and a dash of basil.
Add parmesan to taste after the desired consistency is reached and immediately turn off the heat. If you add it too soon it will melt into a large clump.
For cream of chicken:
Make your roux and use chicken broth as your liquid.
For cream of mushroom:
Sauté mushroom pieces in your fat. Add the flour and make the roux.
Use cream as your liquid. Optional: Once the mixture is thickened to desired consistency, process in a food processor until smooth.