Sift together flour, soda and salt, set aside. Cream together butter, brown sugar until light. Add egg, continue beating until very light. Mix together dry ingredients and chopped butterfinger, blend into creamed mixture. Drop by half tspful. about 2 inches apart, onto greased baking sheets. Bake at 375 for 8 to 10 minutes, or until browned. Remove from baking sheets and place on a wire rack to cool.