Using the flat beaters of an electric mixer, cream sugar and butter for two minutes on low speed. Add 2 1/2 cups of the flour and mix thoroughly.
Turn out cookie dough onto a surface dusted with remaining 1/2 cup of flour. Knead dough until it cracks on surface.
Roll out dough to 1/4-inch thickness, and cut into rectangles with a paring knife, or cut into pleasant shapes [Scottie dogs are a favorite] with cookie-cutters. Prick cookies with fork tines and place on ungreased cookie sheets.
Sprinkle cookies lightly with maple sugar powder, vanilla sugar, or cinnamon sugar.
Bake at 275° for about 45 to 55 minutes, or until lightly browned.
Makes about 2 dozen shortbread cookies.