Preheat oven to 350 degrees. Line 2 baking sheets with parchment paper.
Using your KitchenAid Standing Mixer, using the medium size bowl combine the softened butter, light brown sugar and white granular sugar and mix on low with the wire attachment for 3-4 minutes.
Next, add in the eggs and vanilla and mix for another minute.
In a separate large bowl, add the flour, cocoa powder, baking soda and salt and stir with a spoon to mix.
Add the flour mixture to the wet mixture and use your KitchenAid Standing Mixer to mix on low speed until all ingredients are well combined.
In a separate medium size bowl, combine the semi sweet chocolate chip morsels, peanut butter chips, white chocolate chips and Reese's Pieces and stir to until they are evenly distributed.
Gently stir in 3/4 of the candies into the cookie batter, setting the rest aside until after the cookies are done.
Scoop 2 Tablespoons of cookie dough for each cookie and shape into a ball by rolling between the palms of your hand. Note that the cookie dough is going to be more on the soft side so take care to roll them into balls.
Place each ball on the cookie sheets, about 2 inches apart.
Bake for 14 minutes, until set. Note that when you remove your cookies from the oven, they are going to be soft and may not appear to be done. They are done and will firm up as they cool.
Take the remaining candies and gently press into each cookie. This makes the cookies look extra appealing!
About 10 minutes after pulling the cookies out of the oven, transfer to a cooling wrack and let them cool completely.
Store in an airtight container.