In a 3- to 4-quart pan, combine onion, thyme, sage, and butter. Stir often over high heat until onion is lightly browned, 3 to 4 minutes.
In a small bowl, blend about 1/2 cup broth with the cornstarch. Pour remaining broth and the turkey drippings into pan with the onion mixture. When it boils, add the cornstarch mixture, a portion at a time, until gravy is as thick as desired. Add salt and pepper to taste.
Nutritional analysis per 1/4-cup serving.