Preheat your oven to 350 degrees F. Line a baking sheet with parchment paper or a silicone mat. Set aside.
In a large mixing bowl, beat the butter, sugar, and brown sugar until fluffy, about 1 minute. Add the eggs, one at a time, mixing after each addition. Then add the vanilla and mix. Scrape the sides of the bowl as needed.
In a medium mixing bowl, stir together the flour, salt, and baking soda. Add the dry ingredients to the wet ingredients and mix until just combined.
Using a rubber spatula, stir in the dark chocolate chips and hazelnuts by hand until evenly incorporated.
Use a small cookie scoop (or 1 tablespoon measuring spoon) to portion the cookie dough onto the prepared baking sheet 2 inches apart. These cookies will spread.
Bake for 10 minutes, or until the cookies are set and the bottom edges are golden brown.
Carefully remove the cookies from the oven. Allow them to cool on the pan for 2 minutes before transferring to a wire rack to cool completely.
Notes
I like to gently press extra chocolate chips and hazelnut pieces into the top of the cookie dough balls before baking. This lets you easily see what ingredients are in the cookies. You don't have to do this, but it does make for pretty cookies.