Add the butter to a large microwave-safe glass bowl. Place into the microwave and cook for 20-25 seconds, until melted.
Add the popcorn kernels and coat them evenly in the butter. Place a microwave-safe lid or plate over the bowl and place it into the microwave. Cook for 3 minutes - 3 minutes & 30 seconds, or until the popping slows down to about 4 seconds between each pop, being very careful not to over-cook the popcorn. Side Note: My popcorn took 3 minutes.
Season with sea salt and more melted butter if desired. Serve immediately. Enjoy.