Fill your blender with the amount of oats you would like to turn into flour. 1 cup of quick oats makes just under 1 cup of oat flour. (If you are making just 1 cup, add 1 cup of quick oats + 2 tbsps).
Make sure you have enough oats in the blender to fully cover the blades. You may need to add more oats if it's not blending well.
Blend
Blend the oats for 30 seconds up to 1 minute or until it turns to flour. There should be a light flour powdery texture to it. If there are any oat chunks, keep blending. See photos for reference.
Store
Oat flour can be made on demand if needed, but it also stores beautifully in a jar for up to 3 months.