How to Make It
Line a rimmed baking sheet with parchment paper, and coat with cooking spray.
Combine sugar, water, miso, and butter in a large saucepan. Bring to a simmer over medium-high; cook, whisking occasionally, until golden brown, 13 to 15 minutes. Remove from heat; whisk in vanilla and baking soda. (Be careful; mixture will become very foamy.)
Combine popcorn, pretzels, and vanilla wafers in a large heatproof bowl. Generously coat 2 rubber spatulas with cooking spray. Working quickly, pour caramel over popcorn mixture, and mix gently with rubber spatulas until thoroughly coated.
Spread mixture on prepared baking sheet, and sprinkle evenly with salt. Cool to room temperature, about 20 minutes. Break into pieces.