Line an 8 x 8-inch square pan with parchment paper. Set aside along with an extra sheet of parchment paper.
In a large pot over medium heat, whisk together the peanut butter, brown rice syrup, coconut oil, and sea salt for 3 to 5 minutes, or until smooth and glossy.
Remove from the heat and whisk in the vanilla.
Next, stir in the crispy rice cereal (see note***) and marshmallows (if using).
Transfer the mixture to the prepared pan. Place another sheet of parchment paper on top and use your hands to press and compact the mixture into an even layer in the pan.
Transfer to freezer to begin to firm and cool.
Meanwhile, prepare the peanut butter chocolate topping. Melt the chocolate chips and peanut butter in a double boiler over low heat until smooth and glossy. Remove from heat once melted.
Pour the topping over the chilled bar. Return the pan to the freezer for 15 minutes, or until the chocolate layer has set.
Slice into 25**** small squares. Store in the refrigerator for up to one week or freeze for up to two weeks.