Line a 9 x 13-inch baking pan with a sheet of parchment paper with overhang to allow for easy removal.In a large saucepan over low heat, melt the butter. Add the marshmallows and cook, stirring continuously, until the marshmallows are completely melted. Remove from the heat and stir in the peanut butter. Add the cereal and stir until completely coated. Using a buttered spatula, press the mixture evenly into the prepared pan; set aside.

In a medium saucepan over medium heat, combine the sugar and water. Cook until the sugar has completely melted. Increase the heat to medium-high and cook without stirring until the caramel turns a deep amber, about 5-10 minutes. Be careful not to let the caramel burn. Remove from the heat and add the cream, butter, and salt (the mixture will bubble vigorously). Return the pan to low heat and stir until the sugar lumps have dissolved and the mixture is smooth. Pour the caramel over the crisp layer, spreading evenly with an offset spatula. Allow to cool completely (you can also place it in the refrigerator to speed up the cooling).

Once the crisp/caramel base is completely cool, remove it from the pan using the parchment overhang and place it on a cutting surface. Using a sharp knife, cut into 48 rectangles. Using your index fingers and thumbs gently press the outside corners of the rectangle in to lightly compact the crisp layer while slightly rounding the edges. Continue with the remaining rectangles.

Place the chocolate and the shortening in a bowl set over a pan of simmering water. Cook, stirring occasionally until completely melted. When ready to coat, reduce the heat to low to keep the chocolate warm. Place a crisp/ caramel rectangle on the tines of a fork. Gently lower the bottom into the chocolate to coat the bottom; use a spoon to spoon some melted chocolate over the top and sides of the bar. Lightly tap the fork on the edge of the bowl to let as much excess chocolate drip off. Place the candy bar on a sheet of parchment paper; continue with the remaining bars. Allow the chocolate to set and cool completely before serving and storing. Wrap individually as gifts and treats or store in an airtight container. Enjoy!