Place white chocolate in a microwave-safe bowl and microwave at full power in 10-second intervals, stirring between each one, until melted. Add matcha and stir until completely incorporated. Place the popcorn in a large bowl and drizzle with the white chocolate mixture, tossing as you go, until popcorn is evenly coated. Season with salt. Set popcorn in refrigerator until white-chocolate coating has firmed, about 10 minutes. Break up any clump and serve. Popcorn can be stored in a zipper-lock bag in the refrigerator overnight.
