In a large bowl, combine flour, cocoa powder, baking powder, and salt until evenly combined. Set aside.
In the bowl of a stand mixer or a mixing bowl and hand mixer, cream together the butter and sugar until light and fluffy.
Mix in the egg and vanilla extract until well combined.
Slowly add in the dry ingredients, mixing until just incorporated.
Fold in the Reese's peanut butter chips and chocolate chips.
Scoop out the cookies onto parchment-lined baking sheets and bake at 350°F for 8-9 minutes.
Let the warm cookies cool for 5 minutes before transferring them to a wire rack to cool completely. Enjoy!