Melt chocolate, peanut butter, and butter together over low heat, stirring constantly to avoid burning
Add Diamond Crystal kosher salt and vanilla paste to the melted mixture and stir well
Spread the Chex cereal on a lined baking sheet
Pour the chocolate-peanut butter mixture over the cereal and toss to coat evenly
Chill in the refrigerator for about 15 minutes until partially set
Transfer the mixture to a bag and add powdered sugar
Shake the bag to coat the cereal pieces with powdered sugar
Repeat adding and shaking with powdered sugar until evenly coated
