Preheat oven to 350 degrees Fahrenheit.
Line the cookie sheet with parchment paper and set aside.
In a medium mixing bowl, add flour, baking powder, and cream of tartar. Whisk to combine.
In the bowl of a stand mixer, fitted with a paddle attachment, add butter, peanut butter, brown sugar, and powdered sugar, and mix well.
Scrap down the sides of the bowl.
Add vanilla and eggs and mix well. Scrap down the sides of the bowl.
Using a rubber spatula fold in chopped Reese’s Peanut Butter cups.
Using a large cookie scoop, scoop cookie dough into 10 balls.
Spread evenly on the prepared cookie sheet.
Using the bottom of a flat glass or measuring cup, flatten the cookie to about ½ inch thickness.
Bake cookies for 10 minutes and allow them to cool completely after baking.
To make cookie topping, melt peanut butter chips and oil in the microwave in 30-second increments, stirring in between.
Using a spoon, pour peanut butter over the top of each cookie
Sprinkle with chopped Reese peanut butter cups.
Enjoy!