Popcorn Flour??

To make popcorn flour, grind popped popcorn in your blender or food processor. Put a handful of popped popcorn in the blender. Turn the blender on Low. For medium-ground texture, leave the blender on for about 20 seconds. For finely-ground texture, leave blender on for 30 to 40 seconds. Grind several cupfuls and store in a tightly covered canister or jar so you’ll always have ground popcorn on hand when a recipe calls for it.

from Google