Take the pan with roasted turkey drippings and heat it on the stove over medium high heat. Add the All-Purpose Flour (4 tablespoon) to it and stir it all around until it thickens and cooks for about 3 minutes to make the base roux.
Stir in the Butter (1/2 stick) next until they melt in, then slowly pour in the Milk (2 cup) while you keep stirring.
Once the milk is stirred in, take the pan off the heat. Add Apple Cider Vinegar (1 dash) and Kosher Salt (1 pinch) to taste.
Pour the gravy through a fine mesh strainer into a bowl to get out any lumps. Transfer to a gravy boat and serve!