Start by greasing a 9x13 baking dish with non-stick cooking spray.
Next, melt the butter in a large sauce pot or Dutch oven on the stovetop on medium-low heat.*
Stir the vanilla extract and salt into the melted butter.
Add the mini marshmallows to the melted butter mixture, stirring until the marshmallows have fully melted.*
Remove the mixture from the heat, and stir in the creamy peanut butter until it's completely melted.
Then quickly stir in the Rice Krispies cereal.
Spread the crisp rice mixture into the prepared pan with a spatula.
Next, add the chocolate chips to a microwave-safe bowl, and heat on medium power at 30-second intervals, stirring between each interval.
Once the chocolate chips are almost melted, add the shortening, whisking until smooth.
Use a spatula to spread the melted chocolate into an even layer over the Rice Krispies mixture in the pan and let cool before moving on to the final step below. This will allow the chocolate topping to harden up on top.
Once cooled, slice your chocolate peanut butter Rice Krispie treats into squares and enjoy!