Preheat your oven to 350°F (175°C). Grease your baking pan or line it with parchment paper for easy removal.
In a mixing bowl, combine the softened unsalted butter, creamy peanut butter, granulated sugar, and light brown sugar. Cream until light and fluffy.
Add the room temperature egg to the creamed mixture and mix until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, and salt. Gradually add to the wet mixture, stirring until just combined.
Gently fold in 3/4 cup of the Reese's peanut butter chips into the batter, reserving the remaining 1/4 cup for topping.
Spread the batter evenly into the prepared baking pan. Sprinkle the reserved peanut butter chips on top. Bake for 20-25 minutes, or until the edges are golden brown.
Once baked, remove from the oven and allow to cool for about 10 minutes. Transfer to a wire rack to cool completely before slicing into squares.
