Combine butter, basil and garlic salt; divide in half and set aside.  Salt and pepper chicken breasts.  Grill over medium heat turning frequently until internal temperature reaches 160 degrees, approx. 20  minutes. Each time you turn the chicken, top with a small teaspoon of basil butter.  When finished cooking, remove chicken to a platter and top each breast with a dollop from the remaining 1/2 of basil butter.  Serve