Preheat Oven & Line Tray: Preheat the oven to 356ºF (180ºC) fan-forced and line a baking sheet with parchment paper, set aside.
Prepare Mixing Equipment: Set up your stand mixer with the paddle attachment, or prepare a large mixing bowl with an electric hand beater.
Cream Butter & Sugar: Add softened butter and powdered to the bowl and beat on medium-high for 1 minute, scraping down the sides with a spatula.
Incorporate Dry Ingredients: Sift over the flour, cocoa powder and cornstarch into the mixture. Beat on low-medium speed for 30 seconds until a crumbly dough forms. Turn off the beaters and finish bringing the mixture into a dough with your hands of spatula.
Add Chocolate Chips: Gently fold in the chocolate chips until evenly distributed.
Shape Cookies: Scoop out 1 level tablespoon (25g / 0.9oz) of dough per cookie, roll into balls, and place on the baking sheet, do not flatten, keep them as balls, leaving a 2-inch gap between each. Optional: Press a few extra chocolate chips into the tops of the cookie balls before baking.
Bake Cookies: Bake for 12-15 minutes or until the edges and middles are set.
Cool: Let the cookies cool on the baking sheet for 10 minutes then transfer them onto a wire rack to cool completely. Enjoy!