Bring butter to room temperature. Preheat oven to 300 degrees. Cream the butter until it is the consistency of whipped cream. Beat in sugar. Add salt. Add flour in 4 portions (one cup at a time) mixing well after each addition. Turn out onto a floured board and pat or roll to 1/4 to 1/2 inch thick. Cut into shape desired with cookie cutter. Place on an ungreased cookies sheet and bake for about 20 minutes or until lightly browned. Keep your on eye on them, shortbread burns really fast.