How to Make It
Discard the carrots and onions from the roasting pan; reserve the roasted oranges. Strain the pan drippings into a large measuring cup or bowl. Let stand for 5 minutes, then skim off and discard the fat. (Alternatively, use a fat separator.) Squeeze the juice of the roasted oranges into the cup of skimmed drippings.
Place the empty roasting pan over 2 burners. Add the wine and cook over medium-high heat, scraping up the bits stuck to the pan, 1 minute. Pour the liquid into the skimmed drippings and add enough broth to make a total of 4 cups of liquid.
Melt the butter in a large saucepan over medium heat. Add the flour and cook, whisking, until golden brown, 4 to 5 minutes. Whisk in the broth mixture and bring to a boil. Reduce heat and simmer until thickened, 8 to 10 minutes. Season with ¾ teaspoon salt and ¼ teaspoon pepper. Strain, if desired, before serving.