I got this recipe years ago from Kate, a native of Scotland who (as an adult) once took rides with her kids down a flight of stairs on a large cookie sheet. Ha!
1 pound butter
1 cup sugar
3 1/2 cups flour
1/2 cup cornstarch
Cream the butter and sugar. Blend flour and cornstarch and add to the butter mixture. When I make these I stir with my Kitchenaide until the dough just holds together, no longer. Pat the dough into a round and roll out on a lightly floured board to about 1/4" thick. I cut them into 2 1/2 inch rounds and the recipe made about 48. Prick tops with fork all over. Bake at 325 degrees for about 18 minutes. Be careful because you only want them to brown slightly on the bottom for the best shortbread flavor. Store in an airtight container with waxed or parchment paper separating the layers.
The flavor improves with age but these have never lasted more than a couple of days in our house. I was told once that storing shortbread for a few weeks makes the cookies texture and taste incredible but who has that kind of self-control? Certainly not me.