Make-Ahead Turkey Gravy

I found this on the CookThink blog and it was the best idea ever. Not only was it yummy but I didn't have to be in the kitchen once the turkey was done.
3 pounds turkey wings
2 medium onions, peeled, rough chop
1 cup water
2 32-ounce boxes reduced-sodium chicken broth
1 14-ounce can reduced-sodium chicken broth
2 large carrots, chunked
1/2 tsp thyme
3/4 cup quick-mixing (instant) flour*
2 TB butter
1/2 tsp freshly ground pepper or to taste

Heat oven to 400F/205C/Gas 6. Place turkey parts in a large roasting pan or (ella’s way) a large, oven-safe pot or Dutch oven. Scatter on the onions and roast for 1 hour and 15 minutes.

If necessary, transfer turkey and onions to a stockpot. Otherwise, proceed by adding the 1 cup of water to the pot along with the 2 boxes of broth. Add the carrots and thyme. Bring to a boil, reduce the heat and simmer uncovered for 90 minutes. From time to time, skim off any scum that might rise to the surface.

Remove turkey parts. If desired, remove and discard the skin, pull off and save the meat for another use. Otherwise discard the parts.

Strain liquid into a 3 or 4-quart saucepan (I like to use cheesecloth while straining) and simmer 5 - 10 minutes to slightly reduce the liquid and to concentrate the flavors.

Skim off as much fat as possible. If there’s time, refrigerate for several hours or overnight so the chilled fat is easier to remove.

Add flour to the can of broth and whisk until smooth.

Bring the broth in the saucepan to a gentle boil, add the broth/flour mix and boil 3 to 4 minutes to thicken gravy and remove the floury taste. Add butter and pepper; taste for seasoning and adjust if necessary. Refrigerate leftovers for up to one week or freeze for up to six months. Defrost slowly in fridge overnight before reheating.