Spray a 13x9 pan with cooking spray.
In a microwave safe bowl, melt the marshmallows, butter, and peanut butter together. Add Rice Krispies, stirring well to evenly coat. Spread evenly into the prepared pan. Set aside.
In a large microwave safe bowl combine the butter and peanut butter. Cover with plastic wrap. Microwave for 2 minutes on high. Stir and microwave on high for 2 more minutes. Be careful when you remove from the microwave, it is very hot. Add the vanilla and powdered sugar and stir to combine. Spread over the 1st layer. Sprinkle the mini peanut butter cups over the fudge, lightly pressing down. Put in the fridge for about 1 hour to cool.
After fudge is a little bit firm, make the second layer of Rice Krispie Treats.
In a microwave safe bowl, melt the marshmallows and butter together. Add Rice Krispies, stirring well to evenly coat. Lightly press the cereal together and spread onto of the fudge layer.
For the chocolate layer, melt the peanut butter and chocolate in the microwave, stirring ever 45 seconds. Once melted, pour over the Rice Krispie treats. Gently shake the pan to evenly distribute the melted chocolate mixture.
Place back in the fridge for about 30 minutes for the chocolate to harden. Cut and serve once fully cooled.