Line your 8x8 inch pan with parchment paper, leaving some overhang for easy lifting.
In a microwave-safe bowl, melt the butter in short 30-40 second bursts until just bubbling around the edges, then stir until smooth.
Add the peanut butter to the melted butter and whisk together until the mixture is glossy and fully combined, about 1 minute.
Stir in the sugar and vanilla extract until the sugar starts to dissolve and the mixture becomes thick and fragrant.
Fold in the graham cracker crumbs until the mixture is thick, sticky, and easy to press.
Press the mixture evenly into the prepared pan with a spatula or your fingers, smoothing the top for an even surface.
Chill in the fridge for at least 2 hours, or until firm and set.
Meanwhile, melt the chocolate chips in short bursts in the microwave, stirring until shiny and smooth.
Pour the melted chocolate over the chilled peanut butter layer, spreading it evenly with a spatula for a glossy top.
Return to the fridge for about 30 minutes until the chocolate is set and shiny.
Once chilled, lift the bars out of the pan using the parchment overhang and cut into squares with a sharp knife. Wipe the knife between cuts for clean edges.
Enjoy the chewy, nutty bars immediately, or store in an airtight container in the fridge for up to a week. Serve slightly softened at room temperature for the best texture.
