Preheat oven to 300° F.
Cream the butter. Stir in the sugar until
blended. Sift in the flour and cornstarch. Add the almond or vanilla
extract, if you wish. Stir until the mixture just begins to come
together. Take care not to overwork the dough because this will
cookie tough and shortbread should be delicate.
Pat the dough into a circle about 1/2 inch thick on a highly oiled
sheet. Punch a bunch of holes in the dough with a fork. Bake for
60 minutes, until just beginning to turn golden, but not brown.
wedges while still warm.
From "Sundays at Moosewood Restaurant"