In a large microwave-safe bowl, combine the chocolate and peanut butter. Microwave in 30-second intervals for a total of 1 minute, stirring between, until smooth.
Stir in the marshmallows and microwave again for 1 minute. Mix until fully melted and combined.
Pour in the cereal and gently stir to coat everything evenly.
Transfer to a parchment-lined 9x9 pan and press down to form an even layer.
Let the bars cool and set (I pop mine in the fridge for 30 minutes).
Slice into squares, then toss each one in powdered sugar until coated (tap off the excess).
Store in the fridge or freezer... if you don’t eat the whole pan immediately.