Heat the grease over medium heat in a large cast iron skillet.

Sift in the flour and let it come to a boil for 2 minutes, stirring and mashing down constantly with a flat spatula.

Slowly stir in 11/2 cups of the milk and bring back to a light boil. Continue stirring until the mixture is smooth and reaches the desired consistency, about 2 minutes. You can add more milk or water to thin the gravy, if necessary.