1 cup butter, .5 cup sugar, and 2.5 cups flour.  You cream together the butter and sugar and mix in the flour until just barely combined.  You roll out the dough (maybe 1/4 or 1/2 inch thick), cut it (with cookie cutters or just into wedges), and bake at 300 for 30 minutes.

The texture of shortbread changes a lot depending on how much you mix after the flour is added.