Sift the flour, cornstarch and sugar together in a mixing bowl.  Using a pastry blender, cut in the butter until a soft dough starts to form.  Knead dough until well blended.  Just a minute or two.  Press half the dough into the cookie mold.   Holding the mold upright, tap on a strong edge protected with a folded kitchen towel.  As the dough starts to pull away from the mold, invert over the baking sheet and carefully place the dough on the parchment lined cookie sheet.  Repeat with the remaining dough.

Bake for 35 to 40 minutes or until golden in color.  Immediately sprinkle sugar on top and cool on a wire rack before serving.