1. Grease a 9x13-inch baking pan. Line with parchment paper, then grease the parchment paper; set aside.
2. Make the Bottom Chocolate Layer: Melt together the chocolate chips and peanut butter over a water bath, until completely smooth and melted, stirring every 30 seconds. Pour into the prepared baking dish and, using a spatula, smooth into an even layer. Refrigerate until completely cool and hard, about 30 minutes.
3. Make the Nougat Layer: Melt the butter in a medium saucepan over medium heat. Add the sugar and milk, stirring until dissolved, and bring to a boil. Reduce the heat to low and cook for 5 minutes, stirring occasionally. Remove the pan from heat and add the marshmallow fluff, peanut butter, and vanilla extract, stirring until completely smooth. Fold in the peanuts, then pour over the bottom chocolate layer. Again, refrigerate until completely cool, about 30 minutes.
4. Make the Caramel Layer: Combine the caramels and the heavy cream in a small saucepan over low heat. Melt, stirring occasionally, until smooth. Once completely melted, cook for an additional 4 minutes, stirring frequently. Pour the caramel over the nougat layer. Refrigerate until completely cool, about 30 minutes.
5. Make the Top Chocolate Layer: Melt together the chocolate chips and peanut butter over a water bath until completely smooth and melted, stirring every 30 seconds. Pour over the caramel layer and, using a spatula, smooth into an even layer. Refrigerate until completely cool and set, 30 to 60 minutes.
6. Run a small sharp knife along the edges of the pan to be sur the sides don't stick. Slam the pan upsdie on to a piece of parchment paper (should po right out). Peel away the parchment liner and cut into 32 pieces (I run a long serated knife unfer hot watr, dry it then cut - repeat). Store the bars in the refrigerator and take out 15 minutes before serving (the caramel layer can get a little overly melty if left out too long).