Preheat the oven to 350 degrees.

In a large bowl whisk together the flour, cocoa powder, cornstarch, baking soda, and salt. Set aside.

In another large bowl cream together the butter and brown sugar.

Beat the Nutella into the butter mixture until well combined.

Add in the egg and the vanilla and mix well.

Add the flour mixture to the butter mixture and mix until just combined.

Fold in the chocolate chips.

Scoop the cookie dough by 1 1/2 inch balls and place them 2 inches apart on a baking sheet.

Bake for 10-12 minutes or until the tops look set. Remove from oven and cool for 2-3 minutes on the baking sheet before removing them to a wire rack to cool completely.