Heat broiler. Spray broiler pan with nonstick cooking spray. Place chicken breasts, boned side up, on broiler pan. In small bowl, blend remaining ingredients. Broil chicken 5 minutes 4 to 6 inches from heat. Turn chicken over and spread evenly with sour cream mixture. Broil about 2 minutes more or until topping is puffed and lightly browned and chicken juices run clear. (Meat thermometer should read 170 degrees F.)