1. Preheat the oven to 350°F. Line a large baking sheet with parchment paper.

2. Using an electric mixer, cream together the butter and sugar in a mixing bowl until light and fluffy. In another bowl combine the flour, 1 cup of the oats, the salt, and cinnamon. Add to the butter mixture, stirring with a wooden spoon just until combined.

3. Finely grind the remaining 2/3 cup oats in a blender or food, processor. Dust a pastry cloth or other flat rolling surface with some of the ground oats. Divide the shortbread dough in half. Roll out each half into a circle about 8 inches in diameter and 3/8 inch thick. Sprinkle the remaining oatmeal over the top of the dough and press it into the surface with the rolling pin.

4. Using a sharp knife, cut each circle into 8 wedges. Prick each wedge all over with the tines of a fork. Transfer to the prepared baking sheet. Bake until golden brown, 18 to 20 minutes. Cool on a wire rack, then store in an airtight container up to 1 week.