Preheat your oven to 350°F (175°C). This ensures that your Reeses Pieces Bars bake evenly and come out perfectly golden brown.
Grease a 9x13 inch baking pan or line it with parchment paper for easy removal later. This will make slicing and serving a breeze!
In a large mixing bowl, use an electric mixer to cream together the softened butter and brown sugar until the mixture is light and fluffy. This step is crucial for achieving that soft, chewy texture!
Mix in the creamy peanut butter until well combined. Then, add the eggs one at a time, followed by the vanilla extract. Beat until everything is fully incorporated.
In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, mixing until just combined.
Gently fold in the Reeses Pieces and chocolate chips. Make sure they are evenly distributed throughout the batter for that perfect bite.
Pour the batter into the prepared baking pan and spread it evenly. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the pan from the oven and let it cool in the pan for about 10 minutes. Then, transfer the bars to a wire rack to cool completely before slicing them into squares.