Place butter (not softened) in a large mixing bowl. Add flour, sugar and corn starch. Mix with hands (do not use a mixer) until blended and most of dough is like course cornmeal. It will be very lumpy.
Spread a portion of the dough into the bottom of a glass pie pan and press firmly into the pan. Add dough until the thickness is about 1/2 inch thick.
Place in oven and bake until edges are golden brown. Remove from oven and use a fork to create perforations. Shortbread will break easily when cooled. Remove from pie pan by placing a plate to cover, then flipping over – shortbread will fall out in one piece.