Preheat oven to 350ºF. Prepare a baking sheet with parchment paper and treat with cooking spray.
In a large bowl, mix hazelnuts, confectioners sugar, cocoa powder, salt and espresso powder.
Add eggs whites, hazelnut and vanilla extract. Using an electric mixer, mix until combined and wet, around 2 minutes.
I like to use an ice cream scoop to scoop the batter out and make them all uniform. Top the cookies with a sprinkling of coarse sea salt.
Bake for 15-17 minutes; you want the tops of the cookies to crack. Serve immediately and enjoy!