Prepare your pan by lining an 8×8-inch baking dish with parchment paper, leaving overhang on the sides to easily lift the bars out later. Make sure the parchment is pressed into corners smoothly.
Make the peanut butter base by combining ¾ cup of the peanut butter, melted butter, graham cracker crumbs, powdered sugar, vanilla extract, and salt (if using) in a large bowl. Mix until thoroughly combined into a thick, uniform dough.
Press the mixture firmly into the prepared pan, creating an even layer. Use the bottom of a measuring cup to compact it, ensuring there are no air pockets or loose areas that could cause the bars to crumble later.
Create the chocolate topping by placing chocolate chips and remaining ¼ cup peanut butter in a microwave-safe bowl. Heat in 30-second intervals at 50% power, stirring between each interval, until completely melted and smooth (typically 1-2 minutes total).
Pour the melted chocolate mixture over the peanut butter layer, spreading it evenly with a spatula to cover the entire surface.
Refrigerate the bars for at least 2 hours or until the chocolate layer is set firm. For best results, allow to chill undisturbed without covering.
Cut into squares by lifting the chilled bars out of the pan using the parchment paper overhang. Use a sharp knife wiped clean between cuts for the cleanest edges.