Preheat oven to 375°F and line 2 large baking sheets with parchment paper and set aside. In a large bowl or stand mixer (highly recommend a stand mixer for this recipe) fitted with a paddle attachement, cream together the butter, sugars, and peanut butter on medium speed for 2 minutes, scraping down the sides of the bowl halfway through.
Add ¾ cup of Reese's Pieces and ¾ cup of chocolate chips, and all of the mini chocolate chips and mix at low speed just until combined, be careful not to overmix. Use a large cookie scoop to portion out the dough on the prepared baking sheets, leaving 3 inches between each (about 6 to 8 cookies will fit on a standard cookie sheet).