Foolproof Turkey Gravy

Melt butter in a medium skillet over medium-high. Whisk in flour. Cook, stirring constantly, until flour turns light brown and has a nutty aroma, about 2 minutes. Gradually add broth and reserved drippings, whisking until smooth. Add reserved vegetables and herbs from turkey cavity. Bring to a boil over medium-high, stirring occasionally. Reduce heat to medium-low; simmer, stirring often, until gravy slightly thickens, coats the back of a spoon, and reduces to 4 cups, about 10 minutes. Pour through a fine mesh strainer into a bowl or gravy boat, and serve.