In a large measuring cup or small pitcher, add the water and evaporated milk. Set aside. Pre-measure all the dry ingredients and place everything within reach of where you will be cooking the gravy. In a 10" cast-iron skillet, on high heat, add the oil or grease and let it heat up a few seconds. Add the salt and pepper. When the oil shimmers it is hot enough. Add the flour and butter; stir with a slotted spatula, sifting the gravy through the slots to combine and remove the lumps. Stir continuously until smooth and creamy looking. Let it continue to cook and darken to golden brown as well as remove the "flour" taste. While stirring, add the milk slowly, being careful of the steam. If any lumps develop, use the spatula to smash them and blend them in. Continue to stir/sift the gravy through the spatula until it thickens and starts to bubble. If it gets too thick, just add more milk. Remove from heat. Serve hot.