Preheat oven to 325 degrees Fahrenheit.
In a mixing bowl, sift together flour and 1/4 teaspoon salt. Add 3 tablespoons sugar and combine.
Cut butter into the dry ingredients with a pastry cutter until the mixture resembles fine crumbs.
Knead dough until smooth. Shape into a ball.
Place the ball of dough onto an ungreased cookie sheet and use fingers to press and flatten the dough into a circle, about 8" in diameter. Use fingers to create a scalloped edge.
Use a large knife to cut dough into 16 wedges. Do not remove wedges, leave them in the circle.
Use a salt shaker to sprinkle the top of the dough lightly with salt. Sprinkle top of the dough lightly with cinnamon-sugar mixture.
Bake shortbread for 25 - 30 minutes in a preheated oven, or until edges are lightly browned and dough in the center is set.
Use a knife to cut along previously formed lines. Allow shortbread to cool for 5 minutes. Use a metal spatula to remove cookies from pan and cool thoroughly on a wire rack.