Place the oats in a food processor or blender. Pulse on and off a few times and then give everything a quick stir/ shake. Blend for about 2 minutes, stopping midway to stir things up, until the oats have a very fine texture. See photos above for reference. It won't end up as powdery and fresh as all-purpose flour and will still have very fine chunks still left in it.
Store in an air tight container and use in your favorite oat flour recipes!
Notes
*this can also be done with quick cooking oats or even steel cut oats as desired. If needed for your diet, make sure that you buy *certified* gluten-free oats