Add 2 cups of turkey or chicken stock to a small saucepan with the fresh thyme and bring to a boil. Reduce the heat to a medium-low. Remove the sprigs of thyme.
Transfer about 1 cup of the gravy base to a medium bowl and whisk in the arrowroot starch. Whisk well to remove any lumps. Return slurry to the gravy base and whisk over medium-low heat, simmer and whisk until thickened and smooth.
Notes
There won't be tons of drippings from the roast, but pour off any that there is, fat included, scraping up any little browned bits, too. When adding to the broth, you may want to strain it before you add the thickener.homemade turkey stock is best, if you have it on hand, if not, store-bought (gluten-free) will work, too.gravy thickened with arrowroot can tend to be a tad thin, when reheated. You may need to add additional starch with any leftovers