Line an 8-inch or 9-inch square baking pan with aluminum foil or parchment paper and leave enough overhang to lift the bars out later. The lining should sit flat against the corners so the finished slab chills in an even layer.

Combine the melted butter, graham cracker crumbs, and confectioners’ sugar in a medium bowl, then stir in 1 cup (250g) of peanut butter until the mixture comes together. It should look thick and sandy, almost like damp cookie crumbs, and hold its shape when pressed between your fingers.

Press the peanut butter mixture evenly into the prepared pan with a spatula or the back of a spoon. The surface should look compact and level, with no loose dry patches around the edges.

Melt the remaining 2 Tablespoons of peanut butter with the chocolate chips in the microwave or on the stove, stirring until smooth, then spread the mixture over the base. If using the microwave, heat in short bursts so the chocolate turns glossy and fluid instead of stiff or grainy.

Refrigerate the pan until the bars are completely firm, at least 2 hours, then let them stand at room temperature for 10 minutes before cutting. The top should feel set but still have a slight give, which helps keep the chocolate from cracking.

Serve the bars chilled and cover leftovers tightly before returning them to the refrigerator for up to 1 week. The texture stays fudgy and the layers hold their shape best when stored cold.