Start by placing the strained fat into a skillet and cooking it on low heat. Gradually add the flour, and keep mixing as you go. Once the flour has been completely added and mixed, continue cooking on a low heat until it begins to bubble and appears brown in texture.
Next, remove the skillet from the heat, and slowly mix in the milk. Do this slowly while stirring. Once all of the milk has been added, place the skillet back on the burner, and boil for a minute while stirring. The gravy should thicken. This is the time to add your powders and the salt. Stir until fully mixed, and cook until the gravy is the desired texture or thickness. You can add your homemade gravy directly to a dish or you can place it in a separate serving tray.
Once you have mastered this recipe, you can experiment with different consistencies for your gravy, and consider adding ingredients like rosemary and thyme. The best way to personalize any recipe is to first master its basic form and then play with the ingredients.