Start by lining your 9x9-inch baking dish with parchment paper. This will help you lift the bars out easily once they are set.
In a large mixing bowl, combine the melted unsalted butter and Ritz cracker crumbs. Stir until the crumbs are fully coated and the mixture resembles wet sand.
Next, add the powdered sugar to the crumb mixture. Mix well until fully incorporated. The mixture should be slightly sticky.
Now, stir in ¾ cup of creamy peanut butter until the mixture is smooth and well combined. The peanut butter adds a rich flavor and binds the bars together.
Press the mixture evenly into the bottom of your prepared baking dish. Use a spatula to smooth it out, ensuring it is packed down firmly.
In a microwave-safe bowl, heat the chocolate chips in 30-second intervals, stirring in between until fully melted and smooth. Be careful not to overheat.
Pour the melted chocolate over the peanut butter base, spreading it evenly with a spatula.
Drizzle the remaining 2 tablespoons of peanut butter over the melted chocolate, and use a knife to swirl it for a beautiful marbled effect.
Place the baking dish in the refrigerator for at least 2 hours or until the bars are completely set.