Combine flour, cocoa powder baking soda and salt in a medium bowl and set aside. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed until smooth. With the mixer still running, gradually add sugars. Add eggs one at a time, beating well after each addition; add in 1 cup chocolate-hazelnut spread and vanilla extract; mix until well combined. Turn mixer to low speed and gradually add the flour mixture to the creamed mixture until just combined. Cover mixing bowl with cling wrap refrigerate dough for at least an hour.
Preheat oven to 350°F. Line two or more baking sheets with parchment and set aside.
Spread chopped hazelnuts into a shallow bowl or dish. Shape the cookie dough into 2 inch or walnut-sized balls and roll in the chopped nuts. Place 2 inches apart on the lined baking sheets. Bake 12-14 minutes; remove from oven and let cool on pans about 5 minutes,. Remove to wire racks to cool completely.
When cookies have cooled, spread about a 2-3 teaspoons of the remaining chocolate-hazelnut spread onto the bottom of a cookie, then top with another cookie to form a filled cookie sandwich.