• Prepare a large rectangular baking pan by greasing it with butter or baking spray and lining it with parchment paper. Set it aside.
• Heat a large pot over medium-low heat and add the butter. Once the butter begins to melt, add the peanut butter. The peanut butter will melt with the butter and you'll be able to stir it together.
• Add the marshmallows and let them melt in the hot peanut butter mixture. Use a silicone spatula to stir gently until the mixture is smooth and no marshmallow pieces remain.
• Remove the pot from the heat and add the Rice Krispies cereal, stirring it into the hot marshmallow mixture immediately. Stir until the cereal is all coated.
• Grease the spatula and pour the mixture into the prepared pan, pressing the mixture into the pan and smoothing out the top so it's even.

For the topping:

• Chop the chocolate into small pieces and add it to a microwave safe bowl.
• Melt the chocolate in the microwave on 50% power for 30-second increments until fully melted. Be sure to stir every 30 seconds or so.
• Add the peanut butter to the melted chocolate and stir until combined.
• Spread the melted chocolate over the Rice Krispie treats using an offset spatula or a knife, and smooth it out as best you can.
• Let the pan sit at room temperature for 1-2 hours until the chocolate is set.
• To set more quickly, place the pan in the fridge to set for about 30 minutes.
• Slice and serve.