Preheat oven to 375 °F. In a small bowl, combine flour, baking soda and salt; set aside. In a large mixing bowl, cream together butter and sugar until creamy. Beat in egg until light and fluffy. Gradually blend in flour mixture. Stir in Butterfinger chips. Drop by rounded measuring tablespoonfuls about 2 inches apart onto ungreased cookie sheets. Bake 11 to 13 minutes or until cookies are lightly browned. Cool 2 minutes on cookie sheet; place on wire cooling racks. Store in tightly covered container.