Line an 8x8” square baking pan with parchment paper and spray with nonstick spray. Set aside.
Place the puffed brown rice cereal in a large mixing bowl.
In a small saucepan, combine the peanut butter, maple syrup, coconut oil, and salt if using, over medium-low heat. Whisk to incorporate and melt the coconut oil, and then bring to a boil. Turn down to a simmer and let bubble for 3 minutes, whisking the whole time.
After 3 minutes, remove from the heat and pour over the brown rice cereal. Stir to combine completely, making sure to coat all of the cereal.
Pour the mixture into the prepared pan and use your hand or a spatula to press the bars down firmly. Set aside to let them firm up.
While the bars firm up, place the chopped dark chocolate and peanut butter in a microwave safe bowl and microwave in 30 seconds increments, stirring between each, until it’s smooth and melted.
Spread the chocolate over the peanut butter crispy bars. If using, garnish with peanuts and flaky sea salt.
Let firm up in the fridge for at least 30 minutes before cutting into 16 squares. Store in the refrigerator.