Preheat the oven to 400°F. Lightly grease an 8" round cake pan or springform pan.

Grind the oats in a blender or food processor until they are a fine powder (skip this step if you are using oat flour).

If you are using a food processor, add the flour, confectioners sugar, and salt to the processor bowl and pulse a few times. If you don't have a food processor add the oat flour and the dry ingredients to a mixing bowl and whisk them together.

Add the butter and blend the ingredients together either by pulsing the food processor or by using an electric mixer. The batter should come together in a smooth mass.

Press the dough into the prepared pan and use a knife to score it into 16 wedges.

Bake for 10 minutes at 400° then reduce the oven temperature to 250° and bake for 25 to 30 minutes until golden brown.

Remove the shortbread from the oven and turn the oven off. Using a sharp knife, cut along the scored lines while the shortbread is still hot. Place the pan back in the oven but do not turn the oven on. Let the shortbread sit in the oven with the door closed for 1 hour while the oven cools down (this will let the shortbread dry out and develop a crisp texture).

Remove the shortbread from the oven and allow it to cool completely.