Planning Tip: Can be made 2 days ahead. Reheat in a saucepan over medium-low heat or in the microwave. I found this in Woman's Day magazine. I have not tried this recipe, but I'm posting it for safe keeping.
Melt butter in a large saucepan. Add onion and cook, stirring occasionally, 6 minutes or until tender. Add mushrooms and cook 5 minutes or until tender.
Pour 1 can broth into a medium bowl and whisk in flour until blended. Stir into mushroom mixture in pot. Stir in other can of broth and the thyme; bring to a boil over medium-high heat, stirring frequently.
Reduce heat and simmer 7 minutes, stirring occasionally, until slightly thickened. Stir in pan drippings from turkey if desired and heat through.