Line two to three baking sheets with parchment paper.
In a small bowl, combine the flour, baking powder, baking soda and ½ tsp. salt and set aside.
In the bowl of a mixer fitted with the paddle attachment or by hand with a spoon, mix butter, granulated sugar and brown sugar until just combined.
Add vanilla extract and eggs, one at a time, scraping down between each addition. Mix until combined.
On low, add the flour mixture. When the flour is halfway incorporated add the chocolate chips and hazelnuts. Mix until thorough combined.
Scoop cookies, about 2 Tbsp each, onto prepared cookie sheets leaving about 1 inch between each. Sprinkle generously with large flake salt. Chill cookies in the refrigerator for 60 minutes (optional but recommended).
While the cookie dough chills, preheat the oven to 350°F. Bake cookies until light golden brown, about 15 – 17 minutes, rotating halfway through baking time.