Preheat oven to 350. Cream together the Nutella, egg and brown sugar. Add the flour and mix til just combined. Scoop walnut sized balls of dough into a sheet, a few inches apart. Sprinkle about a 1/4 teaspoon of sea salt on each batch of about 9. Bake for 10 minutes. The cookies will slightly spread but still look very fluffy when you pull them from the oven. Let them sit and cook about 5 minutes before transferring to a cooling rack.