Flour, salt and pepper the chicken and pound between wax paper until very thin, adding a little additional flour. In a very hot frying pan with 1 tablespoon, saute chicken for about 1 minute on each side. Remove to platter. In same pan, adding a little more oil, saute onions adding mushrooms after a few minutes and then the garlic near the end. If browned bits on bottom get too dark, add a little chicken broth and scrape bottom. When onions are good and wilted and mushrooms start browning, add Marsala wine and remaining broth. When mixture returns to a boil, sprinkle Wondra flour gradually, stirring, until thickened. Boil for 1 minute. Return chicken to pan briefly, turning, just to warm, then return entire dish to platter. Serve with parsleyed fettucine or rice