Lightly grease a 9 x 13 pan or line it with parchment paper.
Melt the butter and peanut butter together in a large pot that is big enough for mixing. Heat over medium heat until smooth and liquid.
Remove from the heat. Add the vanilla extract and marshmallows and mix until they melt in.
Add the marshmallows and stir until they melt into the peanut butter mixture.
Add the Rice Krispies and mix until coated.
Scoop the mixture into the prepared pan and flatten out. I use the back of a spoon to flatten it. You can spray the spoon with cooking spray to make sure it doesn't stick.
Melt the chocolate in a microwave-safe bowl in 2 30-second increments stirring in between. Then microwave for 15 seconds at a time, stirring, checking, and repeating until the chocolate is mostly melted. Stir to melt the remaining chocolate.
Pour the melted chocolate on top of the Rice Krispie mix in the pan. Spread it out in an even layer.
Refrigerate for 20-30 minutes or until the chocolate is set.
Slice in 24 and serve.I like to use the parchment paper to help remove the entire bar to a cutting board to slice. You can then put the squares back into the pan.
Video
Notes
Stir the peanut butter and butter continuously while melting to ensure it doesn't burn.Let the Rice Krispie treats set in the fridge before slicing them into squares for clean edges.Substitutionspeanut butter: I use creamy peanut butter, but you can try chunky peanut butter instead. Natural peanut butter isn't sweet like creamy peanut butter but you can try for a less sweet, more peanut-forward flavor.chocolate: you can use whatever chocolate you prefer, I like 50% dark chocolate for a less sweet treat. You can also garnish the top by dropping ingredients into the melted chocolate layer. Try chopped peanuts or chopped peanut butter cups. Try white chocolate chips or butterscotch chips for an extra sweet treat.Store leftovers at room temperature in an airtight container or wrapped in plastic wrap. Eat within a few days. You can also store it in the fridge and let come to room temperature just before serving.