This recipe is from one of our most beloved books: King Arthur Flour's Whole Grain Baking (Countryman Press, 2006; p. 332-333).
"Shortbread, a combination of flour, sugar and butter, with a bit of salt for seasoning, is about the simplest cookie dough you can make. Normally made with all-purpose flour, we make it here with oats, formerly the staple cereal crop of Scotland, the birthplace of shortbread. Oats and butter, the two major ingredients in this recipe, were so common in medieval Scotland that they were considered food for the poor. Thus, oat shortbread was a ubiquitous dish throughout the country, where it was typically baked in celebration of the winter solstice: It's round shape was thought to mimic the sun. We've updated this version with more sugar and a touch of vanilla, but's still a tasty, centuries-old throwback."