Prepare a work surface by laying out two 3-feet long pieces of parchment paper, overlapping slightly.
After popping the popcorn, transfer it to a bowl. Lift the popcorn with your hands and shake the bowl lightly so the old maids (unpopped kernels) fall to the bottom. Lift the 4 quarts of popcorn out of the bowl and transfer to a large brown paper grocery bag.
After stirring, return to the microwave for 1 minute. The mixture should be bubbling up furiously by this point. Remove bowl and stir well then return to the microwave for another minute. Repeat this cooking and stirring for a total of 3 more minutes.
Microwave on high power for 1 minute. Remove the bag and hold it at the top and one of the bottom corners. Shake well and return to the microwave for another minute. Repeat cooking and shaking two more times for a total of 4 minutes. Turn the popcorn out onto the prepared parchment paper. Allow to cool completely.
Sprinkle, to taste with flaky sea salt. (Just take a good pinch in between your thumb and forefinger and rub the fingers together to break up the large flakes.)
See Café Tips above in the post for more detailed instructions and tips to ensure success.