Preheat oven to 350°F. With an electric mixer, cream butter and sugar until light and fluffy. Add flour and mix well until a soft dough is formed. Dough may be rolled to 1/4 inch thick and cut with cookie cutters, or divide dough in half and shape each half into a log. If desired, roll dough logs in finely chopped walnuts or pecans , pressing nuts gently into dough. Wrap dough logs in plastic wrap and refrigerate for 30-60 minutes until chilled through and firm but not hard. Slice dough logs into 1/4 inch slices. Place cookies 1-inch apart on cookie sheets lined with parchment paper. Bake for approximately 10 minutes until edges are lightly browned, being careful to not over-bake. Allow cookies to cool on sheets for 3-5 minutes before removing to wire racks to cool completely.