Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.

In a medium bowl, combine flour, cake mix, cocoa powder, cornstarch, and baking soda. Set aside.

In the bowl of your mixer, beat butter and sugars on medium speed until light and fluffy, about 2 minutes. Add eggs, one at a time, until combined, scraping the sides of the bowl as needed. Mix in vanilla extract. With the mixer on medium-low speed, slowly add the flour mixture, scraping the sides of the bowl as needed until combined. Fold in chips and candies.

Using a large cookie scoop, scoop cookies onto prepared baking sheets. Bake for 10 minutes or until edges are set and centers look slightly undercooked. Let cool on baking sheets for 5 minutes before removing to a wire rack to cool completely.