In my opinion the best chicken gravy is made with drippings, not chicken stock; and it is made with milk, not water. This is the gravy my mother made and, after all, she was the world's greatest cook, especially when it came to fried chicken and gravy!
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When chicken is done, remove from pan and set aside; keep warm while making gravy.
Remove all but 1/4 cup drippings from pan. Loosen any crusty bits with a heavy spoon or spatula. Over medium-high heat, stir in 1/4 cup flour and mix with drippings, using a wire whisk.
When thoroughly blended and turned a beige color, gradually begin to add the milk a little at a time, stirring constantly with the whisk. Keep stirring after all the milk has been added, until mixture begins to thicken. When it begins to bubble, turn heat to low and continue cooking for about 2 minutes. Add salt and pepper to taste. Serve with mashed potatoes and fried chicken.