1. Heat oven to 400°F. Have ready a large roasting pan.

2. Arrange wings in a single layer in pan; scatter onions over top. Roast 1 1/4 hours until wings are browned.

3. Put wings and onions in a 5- to 6-qt pot. Add water to roasting pan and stir to scrape up any brown bits on bottom. Add to pot. Add 6 cups broth (refrigerate remaining 2 cups), the carrot and thyme. Bring to a boil, reduce heat and simmer, uncovered, 1 1/2 hours.

4. Remove wings to cutting board. When cool, pull off skin and meat. Discard skin; save meat for another use.

5. Strain broth into a 3-qt saucepan, pressing vegetables to extract as much liquid as possible. Discard vegetables; skim fat off broth and discard (if time permits, refrigerate broth overnight to make fat-skimming easier).

6. Whisk flour into remaining 2 cups broth until blended and smooth.

7. Bring broth in pot to a gentle boil. Whisk in broth-flour mixture and boil 3 to 4 minutes to thicken gravy and remove floury taste. Stir in butter and pepper. Serve, or pour into containers and refrigerate up to 1 week or freeze up to 6 months.