1. Combine first 3 ingredients in a shallow dish. Dredge chicken in flour mixture.
2. Melt 2 tablespoons butter or margarine in a large skillet over medium-high heat. Add chicken, and cook 5 minutes on each side or until done. Remove and keep warm.
3. Melt remaining 1 tablespoon butter or margarine in skillet over medium heat. Add onion and mushrooms, and cook, stirring occasionally, 3 to 5 minutes or until tender. Sprinkle with 1 tablespoon flour, and cook, stirring constantly, 1 minute. Add wine, and cook 1 minute, stirring to loosen particles from bottom of skillet; add broth and thyme. Bring to a boil over high heat, and cook, stirring often, 2 minutes or until thickened. Serve sauce over chicken.
* 1/3 cup low-sodium fat-free chicken broth may be substituted.