Line a 9x9-inch square baking pan with parchment paper, ensuring an overhang on two sides for effortless removal.

In a large mixing bowl, whisk together the graham cracker crumbs and powdered sugar until no large lumps remain.

Add the 1 cup of creamy peanut butter and the melted butter to the dry mixture.

Stir using a heavy spatula until the ingredients are fully integrated and form a thick, uniform dough.

Transfer the dough to the prepared pan and press firmly into an even layer using the bottom of a flat measuring cup.

Combine the semi-sweet chocolate chips and the remaining 2 tablespoons of peanut butter in a microwave-safe glass bowl.

Heat the chocolate mixture in 30-second increments, stirring after each interval until the chocolate is completely smooth and glossy.

Pour the melted chocolate over the peanut butter base and use an offset spatula to spread it evenly to the edges of the pan.

Place the pan in the refrigerator for at least 1 hour, or until the chocolate topping has fully set.

Lift the slab out of the pan using the parchment handles and slice into 24 squares using a sharp, warm knife.