My favorite candy growing up, and maybe still today, is Reese's Pieces. Since I no longer go trick-or-treating, I decided to get my candy fix from dark chocolate cookies studded with the peanut butter filled candy pieces. I use special dark cocoa powder (a Dutch-processed cocoa) for intense chocolate flavor, and brown sugar to ensure the perfect chewy cookie.
Position an oven rack in the center of the oven and preheat to 350 degrees F. Line a baking sheet with parchment paper.
Whisk the warm butter and chopped chocolate together in a medium bowl until smooth. Set aside.
Whisk the flour, cocoa powder, baking soda, baking powder and salt together in another medium bowl.
Combine the brown sugar, granulated sugar and butter-chocolate mixture in a stand mixer fitted with the paddle attachment. Beat on medium speed until combined, 1 to 2 minutes. (It will look like it's separating but will come together once you add the eggs.) Beat in the eggs one at a time, beating well after each addition. Beat in the vanilla. Continue beating until the mixture is combined and creamy, 1 to 2 minutes. Slowly add in the flour mixture on low speed and mix until you no longer see any flour bits, about 1 minute. Stir in the 1 1/2 cups Reese's Pieces by hand.
Using a 1 1/2-tablespoon ice cream scoop, scoop the batter onto the prepared baking sheet, leaving 2 inches between cookies; the baking sheet should hold about 8 cookies. Dot each cookie with 2 to 3 of the remaining Reese's Pieces. Bake on the middle rack until puffed and set in the middle, about 10 minutes. Let cool slightly on the baking sheet before transferring the cookies to a cooling rack to cool completely. Repeat with the remaining dough.