Meanwhile, melt butter in large saucepan over medium heat. Whisk in flour until smooth. Cook, whisking frequently, until peanut butter–colored, about 5 minutes. Slowly whisk in 3 cups turkey stock until no lumps remain. (Remaining stock can be refrigerated for up to 2 days or frozen for up to 2 months.) Whisk in wine, 1½ teaspoons salt, and ½ teaspoon pepper and bring to boil. Reduce heat to medium-low and simmer until slightly thickened and reduced to about 2½ cups, 8 to 10 minutes. Off heat, season with salt and pepper to taste. Cover and keep warm.