How to Make It
Place the 1/4 cup of the popcorn kernels in a medium paper bag (about 10 by 12 inches). Microwave for 2 minutes. Transfer to a large bowl, discarding any unpopped kernels. Repeat with the remaining 1/4 cup of popcorn kernels.
In a medium microwave-safe bowl, combine the butter with the brown sugar, miso, corn syrup, sesame oil and 1/2 teaspoon of salt. Microwave in 30-seconds bursts for about 3 1/2 minutes, until the butter has melted and the mixture is bubbling. Whisk in the baking soda.
Return the popcorn to the paper bag. Scrape the hot miso caramel into the bag along with the sesame seeds. Close the bag and shake well to coat. Roll down the top of the bag, place it in the microwave on its side and microwave for 1 1/2 minutes. Shake the bag and return it to the microwave, placing it on its other side. Microwave for about 1 1/2 minutes, until the caramel is dark brown and the popcorn is crisp.
Line a rimmed baking sheet with wax paper. Shake the caramel corn out onto the prepared sheet. Using a rubber spatula, stir the popcorn to help the miso caramel coat more evenly. Season with salt. Let cool at room temperature for 15 minutes before serving.