Preheat oven to 350 °F (175 °C) and prepare a 9x13-inch pan with parchment paper or grease it lightly.
In a large bowl, mix crispy cereal, graham cracker crumbs, melted butter, brown sugar, and salt until evenly combined.
Press the mixture firmly into the bottom of the prepared pan in an even layer.
Bake for 10 to 12 minutes until set and lightly golden.
Remove the pan from the oven and sprinkle chocolate chips evenly over the warm base.
Add small dollops of peanut butter on top of the chocolate chips if using.
Let the chocolate soften for a few minutes, then spread into a smooth layer.
Refrigerate for at least 1 to 2 hours until the chocolate is firm.
Lift bars from the pan using parchment edges and cut into squares or rectangles to serve.