Line a 11 x 13 metal or glass baking pan with parchment paper so you can easily lift your brownies right out once they are cooled.
In a large bowl, thoroughly mix the peanut butter, melted butter, white sugar and brown sugar together. Slowly add the eggs, vanilla extract, and pinch of salt.
In a separate bowl, whisk the flour and baking powder.
Slowly add the flour and baking powder mix to the peanut butter mixture and slowly mix or fold to combine all ingredients. DO NOT OVER MIX! Over mixing will make fluffy cake-like brownies.
Smooth the batter into the 11 x 13 pan and sprinkle the Reese's Pieces over the batter.
Bake for 30-35 minutes. They will feel firm on top and moist in the center.
Allow them to cool for at least 30 minutes before cutting them
Notes
Nutritional values may vary and are meant to be a guide.