Preheat the oven to 350 degrees F (175 degrees C).
Mix flour, butter, confectioners' sugar, salt, and baking powder together in a bowl using an electric mixer on medium speed until well blended. Pat dough into a 9-inch square baking pan. Sprinkle with cinnamon sugar.
Bake in the preheated oven until edges are golden, 30 to 35 minutes. Cut into bars while still warm.