Add white rice to FourSide jar and secure lid. Press "Speed Up" to Speed 9, and run full cycle. Add rice flour to large bowl or zip-top bag.
Add oats to jar and secure lid. Press "Speed Up" to Speed 7, and run cycle for 20 seconds. Add oat flour, cornstarch, and tapioca starch to rice flour; incorporate all ingredients.
Use immediately or store in zip-top bag in refrigerator or freezer.