Preheat the oven to 350℉. Line baking sheet(s) with parchment paper.

In a large bowl, using an electric handheld mixer on medium speed, mix the softened butter, peanut butter, brown sugar, and white sugar until combined. Add the egg, egg yolk, and vanilla and beat at high speed until fluffy.

In a separate bowl, whisk together the flour, baking soda, baking powder, and salt. Add to the mixing bowl and mix at low speed just until combined. Fold in the chocolate chips and Reese's Pieces.

Roll the cookie dough into balls using about 1 ½ tablespoons of dough per cookie place 2 inches apart on the prepared baking sheets. Bake the cookies one pan at a time in the preheated oven for 8-12 minutes or until puffy and no longer wet-looking on top. Immediately top with additional Reese's Pieces and chocolate chips, if desired. Let cool on the baking sheets for 10 minutes before transferring to a wire rack to finish cooling. Finish baking the remaining cookies. Enjoy!