Beat 2 sticks butter, 1/4 cup granulated sugar and 1/2 cup confectioners' sugar until fluffy. Whisk 2 cups flour and 1 teaspoon salt, then stir into the butter mixture. Press into a buttered 8-inch square or 9-inch round tart pan. Score into wedges, strips, squares or diamonds with a fork, then chill 30 minutes. Bake about 1 hour at 300 degrees. Cool, then slice along the scored lines.