In bowl whisk together flour, cocoa powder, baking soda, cornstarch and salt, set aside.
In stand mixer fitted with paddle attachment cream together your butter and sugars until light and fluffy.
Add in eggs until combined then add in your Nutella and vanilla.
Slowly add in your dry ingredients until just combined then fold in your chocolate chunks.
Cover and refrigerate for about 3 hours (trust me on this).
Preheat oven to 350 degrees.
Take your cookies out of the refrigerator and line a baking sheet with parchment paper or a silpat mat.
Grab aout 2 Tbs of your cookie dough and roll into balls and place them at least 2" apart on baking sheet.
Sprinkle/press sea salt onto tops of cookies and bake I oven for 15-18 minutes until just done on the outside but gooey on the inside.
Remove from oven and sprinkle with more sea salt if desired, let cool on pan for 5 minutes before transferring to cooling rack to cool completely.