1. Preheat oven to 350 degrees F. Line a baking sheet with parchment paper or Silpat baking mat or parchment paper. Set aside.
2. In a medium bowl, whisk together flour, baking soda, sea salt, and cocoa. Set aside.
3. With a mixer, cream butter and sugars together until smooth. Add in eggs, one at a time. Next, add in vanilla extract and mix until combined.
4. Gradually add flour mixture and beat until just combined. Stir in the chocolate chips and hazelnuts. Scoop the dough into rounded tablespoons and place on prepared baking sheet, about 2 inches apart. Sprinkle each cookie with sea salt.
5. Bake cookies for 8-10 minutes, or until cookies are set, but still soft in the center. Don't overbake. Remove from oven and let sit on baking sheet for 3 minutes. Move to a cooling rack and cool completely.