In an electric mixer, beat butter and sugar to a creamy mixture. Gradually add the cornstarch. Beat well. Beat and blend in the flour until very smooth mixture. Drop by small tsp onto ungreased cookie sheet.
Bake in 275-300 degree oven for 30 minutes. Edges should NOT brown (that means they are over done). Baking Shortbread cookies to perfection really is an art. It has taken me years to perfect it.