Cooking is all about measuring ingredients and blending the together to make something new. Gravy is one of the most variable dishes in your recipe book. The ratio of flour to milk has to be just right to result in a thick, creamy and smooth gravy. Seasoned cooks create gravy with a pinch of this and a pinch of that. Successful cooks know the ratio of flour to milk needed to make good gravy.
The Magic Ratio
Well, the ratio isn't magical. To make gravy, you need the same amount of flour that you do fat, whether you use butter or oils. The milk is what makes up the bulk of the gravy. You need 12 times the amount of milk as you do flour to make a good gravy. That makes the ratio 12 to one, milk to flour.
Use 1/4 cup butter or oil of some kind and 1/4 cup flour. When it's time to deglaze the pan or add the milk, slowly whisk in 3 cups of milk. This should make a nice, thick gravy. Add a few extra tablespoons of milk to the gravy to thin it out, one tablespoon at a time. To thicken the gravy, let it simmer a few extra minutes.
For Thickening Sauces
To thicken sauces or gravies that refuse to do so by simmering, use another ratio of milk to flour. For every cup of sauce, add 2 tablespoons of flour to a 1/4 cup of milk and whisk the two ingredients together. When they're well blended, mix the thickener into the sauce. Let it simmer to the desired thickness.
To make the sauce richer, smoother, try adding heavy cream to the gravy. In the ratio, you cut the amount of milk needed in half. Replace one of the halves with heavy cream. Mix both into the gravy and simmer the sauce or gravy to the desired thickness. Then, remove the pan from the heat to prevent the cream in the sauce from collapsing. Another alternative is cornstarch and water or broth, which helps you thicken gravy when you don't have time to let it simmer to your desired consistency. Use 1 tablespoon of cornstarch for every 1 1/2 to 2 cups of gravy in the pan. Use just enough cold water or cold broth to turn the cornstarch into a paste. Whisk this paste into your gravy. Let it simmer for a few minutes before serving to get rid of the chalky texture of the cornstarch.