1. Remove turkey trimmings (giblets, gizzard, neck, etc.). Scrape brown bits off bottom of roasting pan, and pour drippings into a medium saucepan.
2. Add sherry to saucepan, and cook over high heat until liquid has reduced by about half (about 5 minutes).
3. Combine flour and broth in small bowl, stirring with whisk; add broth mixture to pan; bring to a boil, stirring constantly. Reduce heat to medium; simmer 10 minutes, stirring frequently.
4. Add butter, if desired; when it melts, add salt and pepper to taste. Keep warm until ready to serve.