In a mixing bowl, whisk together the flour, cocoa powder, cornstarch, baking powder, baking soda and salt. Set aside.
In a separate bowl, beat together the butter with the brown sugar and granulated sugar with a held hand or stand up mixer until combined and creamy.
Mix in the egg, Nutella and vanilla extract until combined.
Slowly add the dry ingredients into the butter mixture on low speed until just combined. Make sure to scrape down the sides of the bowl with a spatula to make sure that all the ingredients are combined. Be careful not to over mix.
Stir in the chocolate chips.
Cover and refrigerate for at least 30 minutes or up to 24 hours.
When ready to bake, preheat the oven to 350 degrees Fahrenheit. Sit the dough on the countertop to soften while the oven is preheating.
Drop the cookie dough onto baking sheets in approximately 1.5 tablespoon amounts.
Bake for 10-12 minutes until the top of the cookies look set.
Cool on the baking sheet for 5 minutes and then move the cookies to a wire rack to cool completely.
Then the cookies are ready to serve and enjoy!