Preheat oven to 350 degrees.
Add egg and brown sugar to medium mixing bowl and beat with an electric hand mixer for 30 seconds. Add Nutella and flour and beat until combined. Dough will be thick. Cover with plastic wrap and place dough in freezer for 10 minutes.
After 10 minutes, roll dough into 1 inch balls. Place balls at least 2 inches apart on parchment paper lined baking sheet or ungreased baking sheet. Bake for 12 to 14 minutes or until just set. Cookies will be soft and a bit gooey looking. Remove from oven and sprinkle with sea salt. Let cool for a minute or two on baking sheet before carefully moving to cooling rack. Store cooled cookies in air tight container.