Rub the chicken breast with the balsamic vinegar. Then sprinkle one side with salt and pepper and half of the curry powder. Now sprinkle half of th flour on the chicken. In a skillet, heat the olive oil over medium-high heat. Add the chicken, floured side down. Add the remaining curry and flour to the chicken in the pan carefully. Lower the heat to medium. You will want to cook breasts about 5 minutes on each side, depending on how thick the chicken is. (Hint: You can use a rolling pin to thin the partially thawed chicken. Be sure to use wax paper or plastic wrap between the chicken and the rolling pin, though. This is really easy to do when the chicken is still partly frozen.) When chicken is cooked, remove from pan and keep warm. Add chicken broth and, using a wire whisk, whisk up the browned bits of the bottom of the pan. When sauce has reduced slightly, add the lime juice. Allow to cook another minute, then add the butter and cilantro. Once butter has melted and is incorporated into the sauce, it is ready. Pour over the top of the chicken and serve.