Preheat oven to 325 degrees. Lightly butter 9" springform pan. Using electric mixer, beat 1 cup butter in larger bowl until light and fluffy. Add brown sugar and beat well. Using rubber spatula, mix in flour and salt (do not overmix). Press dough into prepared pan. Combine sugar and cinnamon in small bowl. Sprinkle cinnamon sugar over dough. Cut dough into 12 wedges, using ruler as guide and cutting through dough. Pierce each wedge several times with toothpick.
Bake until shortbread is brown, firm at edges and slightly soft in center, about 1 hour. Cool shortbread completely in pan on rack. Remove pan sides. Recut cookie into wedges.