Line an 8x8-inch baking pan with parchment paper, leaving overhang on the sides.
In a large bowl, combine the graham cracker crumbs, peanut butter, melted butter, powdered sugar, vanilla extract, and salt until a thick dough forms.
Press the mixture firmly and evenly into the prepared pan.
In a microwave-safe bowl, combine the chocolate chips and peanut butter.
Microwave in 20-second intervals, stirring between each, until smooth and fully melted.
Pour the chocolate mixture over the peanut butter layer and spread evenly with a spatula.
Sprinkle with chopped peanuts, mini chocolate chips, or flaky sea salt if desired.
Refrigerate for at least 2 hours, or until completely firm.
Lift the bars out using the parchment paper and cut into squares before serving.