Pour turkey drippings into a measuring cup. Skim fat, reserving 1/4 cup; set aside. Add enough broth or water to the drippings to measure 3 cups.
In a large saucepan, saute mushrooms in reserved fat until tender. Add onion powder and rosemary; cook 1 minute longer. Stir in the flour, salt and pepper until blended.
Gradually stir in the drippings mixture. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in browning sauce if desired.