Line an 8×8 or 9×9 inch square baking pan with parchment paper, leaving an overhang on the sides for easy removal. In a medium mixing bowl, combine the graham cracker crumbs, melted butter, and granulated sugar. Stir until the mixture resembles wet sand. Press the mixture firmly and evenly into the bottom of the prepared pan using the back of a spoon or a flat-bottomed measuring cup. Place the pan in the refrigerator to set while you prepare the filling.

In a large mixing bowl, beat the softened cream cheese and creamy peanut butter together using a hand mixer or stand mixer. Continue mixing on medium speed until the combination is smooth and completely free of lumps. Add the vanilla extract and mix again to incorporate the flavor evenly throughout the base.

Turn the mixer to low speed and gradually add the powdered sugar to the peanut butter mixture. Once the sugar is mostly incorporated, increase the speed to medium and beat for 1-2 minutes until the filling is light and fluffy. Be sure to scrape down the sides of the bowl with a spatula to ensure every bit of sugar is blended in.

Gently fold the thawed whipped topping into the peanut butter mixture using a rubber spatula. Use a slow “under and over” motion to keep the air in the topping, which ensures the bars stay light and airy. Continue folding until no white streaks remain and the filling is uniform in color and texture.

Retrieve the crust from the refrigerator. Pour the peanut butter filling over the crust and spread it into an even layer using an offset spatula. Sprinkle mini chocolate chips over the top or drizzle with melted chocolate if desired. Cover the pan with plastic wrap and refrigerate for at least 4 hours, though overnight is preferred for the best texture. Once set, lift the bars out using the parchment overhang, slice into squares, and serve cold.