12 ounces ground pork sausage (we like spicy sausage)
1/4 cup bacon grease or cooking oil
1/4 cup diced onion 2-4 tablespoons all purpose flour
1-2 cups milk 
. In a skillet over medium heat, add the sausage and onion to the bacon grease. Cook while stirring until sausage is brown and onion tender. Push sausage and onion to one side of the skillet. Tilt skillet so oil runs to opposite side (away from onion).
To make roux: Holding the skillet tilted, add one tablespoon of flour to the bacon grease. Stir to dissolve flour. Watch the consistency of the roux and add more flour as necessary to obtain a thin, dull colored paste. There should be no visible liquid grease or lumps of flour in the roux. Add additional oil or flour as needed. You must get the roux consistency correct now. You can NOT add flour or oil after adding the milk in step 4 (flour will lump).
If you want white gravy, go to the next step (adding milk) just as the roux begins to show color. If you want brown gravy cook the roux until it turns a rich brown color (just before burning). You must constantly stir the roux.
Add 1/2 cup milk while stirring. As the roux dissolves and the milk begins to boil, add more milk a little at a time while watching the thickness of the gravy. The thickness will be determined by how much milk you add and how long you cook it. When the gravy is removed from the heat and cools, it will become a little thicker.
As you approach the thickness you want, add salt and pepper to taste and cook one more minute.
If you want the gravy spicy, add a dash of crushed red pepper flakes in the previous step.
Pour the hot gravy over my mama biscuits