Chop chocolate into small chunks and butter into 2-3 pieces, and put both into a microwave-safe bowl.
Melt chocolate and butter on medium power in the microwave, stirring every 30 seconds, until smooth. (It will take around 2 minutes.)
Add peanut butter, vanilla extract, and kosher salt, and mix until smooth.
Pour cereal into a large bowl and add chocolate-peanut butter mixture. Stir gently until all pieces are coated.
Pour confectioners sugar into a large ziptop bag along with the cocoa powder.
Add coated cereal and shake until well coated. You may need to do this in batches.
Spread onto cookie sheet in a single layer to cool.
When cool, put into a large bowl and gently stir in M&Ms and pretzels.
Notes
Ingredient Notes: • You can substitute Crispix for Chex Mix (though in that case, this dessert may not be gluten-free). • Use a regular commercial peanut butter for this recipe, like Jif or Skippy. Natural peanut butters are delicious, but unfortunately they just don’t melt as smoothly as non-natural brands! Note that for peanut-free muddy buddies, you can just leave out the peanut butter in this recipe.How to Store: No refrigeration needed—just keep it in an airtight container, where it will last for about a week.