Place rolled oats in blender and blend at high speed until oats become flour (1-2 minutes).
Use a rubber spatula to scrape down the sides and pulse for 30 seconds longer until the flour is an even consistency.
Remove oat flour from the blender and use it in recipes calling for oat flour or store it for future use in an air tight container away from direct light for 3-6 months.
Notes
The amount of oat flour you end up with will vary based on the type of oats used. For 1 cup of rolled oats, you can expect to get slightly more than 1 cup of oat flour after blending.
The amount of time oat flour will keep depends on the type of oat used and how fresh they are. You can use a piece of masking tape and a pen to write the date you blended your oat flour on the bottom of your storage container.