This is a super easy method for making popcorn salt.
Not really a recipe.
Store bought popcorn salt is regular salt that has been ground very fine. This is done so that it sticks to the popcorn.
No need to buy this since you have everything needed to make it already.
Put one cup of kosher salt into a food processor. 10 3-second pulses should perfectly blend this to the correct consistency.
Store in an appropriate shaker or dredge.