In a medium saucepan, whisk the butter and cocoa powder over medium-low heat until the butter is completely melted and smooth. Whisk often to keep from burning.
Then, whisk in sweetened condensed milk until fully combined.
Add in the soft caramel candy and continue whisking until the caramel is completely melted.
Remove from heat and immediately add in the vanilla extract and mini marshmallows. Fold until the marshmallows are completely melted.
Lastly, fold in the Rice Krispie cereal until the cereal is completely coated in the mixture.
Prepare two baking sheets by lining them with parchment paper.
Coat a large cookie scoop with non-stick spray and use it to scoop out individual cookies onto the prepared baking sheets.
Spray the back of a spoon with non-stick spray and use it to flatten and shape the cookies into a circle.
Refrigerate the cookies for 1-2 hours or until they are set and can easily be removed from the parchment paper.