These are a melt in your mouth variety - really simple to make and rarely make it to Christmas. The cornstarch is the trick to making shortbread soft and melt in your mouth.
1 cup butter (2 sticks) cut in chunks
1/2 cup icing sugar
1/2 cup cornstarch
1 1/2 cup all purpose flour
1/2 tsp. vanilla
Steel Knife: Process butter with icing sugar until well creamed - about 1 minute. Add cornstarch, flour and vanilla. Process with on/off turns just until dough is well mixed and begins to gather together in a ball around the blade.
Shape rounded teaspoonfuls of dough into small balls. Place on ungreased cookie sheet and flatten in a criss-cross pattern with the floured tines of a fork. Bake at 350 F about 12 - 15 minutes or until edges are slightly browned.
Note: The longer shortbread sits, the more flavourful it becomes so three weeks before Christmas is a good time.