Simmer, uncovered, 1 1/2 hours.
Remove the wings and cool. Once cool, remove and discard skin; reserve meat for another use. Strain broth into fat separator or into a bowl. Let sit 10 to 15 minutes until fat rises to the top. Pour defatted broth into a saucepan. You also can put the bowl in the freezer. The fat will rise to the top and become solid. What's left underneath will be jelled, which is what you want.
Whisk flour into remaining 2 cups broth until well blended and smooth. Bring broth in saucepan to a gentle boil. Whisk in flour mixture and cook 5 minutes to thicken gravy and cook out the raw flour taste. Stir in butter and season with pepper.
Nutrition information per ½ cup serving:
Calories50Fat1 gSodium160 mgCarbohydrates6 gSaturated fat1 gAdded sugars0 gProtein4 gCholesterol3 mgDietary fiber0 g
Exchanges per serving: ½ carb, ½ lean protein.