Measure Your Cereal & Prep The Ingredients. This recipe moves quickly once you get started, so make sure you have everything close by and in reach! Measure the cereal into a large bowl and set aside. Line an 8x8 pan with parchment paper and set aside.
Melt Chocolate Peanut Butter Mixture. In a large saucepan, melt butter, chocolate chips, peanut butter and salt together over low heat or medium-low heat, stirring the whole time, until smooth and glossy, with just a few tiny lumps or bumps left.
Stir In Marshmallows and Vanilla and stir over low heat JUST until the marshmallows are melted.
Coat The Cereal. Pour the melted chocolate peanut butter mixture over the Chex cereal and stir to combine, until the cereal is evenly coated in the chocolate mixture.
Dust, Spread & Dust. Sprinkle 2 TBSP of the powdered sugar into the bottom of your prepared pan (I use a fine mesh sieve). Transfer the cereal mixture to the pan and spread into an even layer, packing it down slightly with the spatula. Dust the top of the bars with the remaining 2 TBSP of powdered sugar.
Chill To Set. Transfer the whole pan to the fridge and chill the bars in the refrigerator for at least 1 hour to set up completely.
Slice & Serve. Cut into 9-12 slices and enjoy! Store leftovers in an airtight container in the fridge 3-4 days.