Line your square pan with parchment paper, leaving overhang on sides for easy removal.
In a microwave-safe bowl, melt the peanut butter, melted butter, and sifted powdered sugar together in 30-second bursts, stirring until you get a smooth, creamy mixture that’s slightly thick but spreads easily.
Add the finely crushed graham cracker crumbs to the peanut butter mixture and stir until well combined. The mixture should feel thick and slightly sticky, with a peanut butter aroma filling the air.
Press this mixture evenly into the prepared pan using a spatula or your fingers, creating a firm, even base. Place the pan in the fridge to chill for about 30 minutes.
Meanwhile, melt the chocolate chips with a tablespoon of coconut oil or butter in the microwave in 30-second bursts, stirring well after each until the mixture is shiny and smooth.
Pour the melted chocolate over the chilled peanut butter layer, spreading it out with the spatula to create an even, glossy top. Return the pan to the fridge and chill for at least 2 hours, or until the chocolate is set and firm.
Once the bars are fully set, lift them out of the pan using the parchment overhang. Use a sharp knife warmed slightly to cut into squares, wiping the blade clean between slices for neat edges.
Serve the bars chilled or at room temperature, enjoying their rich, gooey texture and shiny chocolate top. Store any leftovers in an airtight container in the fridge for up to a week.