Preheat oven to 325 degrees F. Spray a 9x13-inch baking pan with nonstick cooking spray and set aside.

In a medium bowl, whisk together flour, salt, and baking soda. Set aside.

In a small saucepan, melt the butter over medium-low heat and continue to cook, swirling occasionally, until butter turns golden brown, Skim foam from top, and remove from heat. Pour into a bowl to stop the cooking, leaving any burned sediment behind; let cool.

In the bowl of a stand mixer, mix the browned butter and sugars together until combined. Add the eggs and vanilla extract and mix until smooth. Slowly add the dry ingredients and mix on low, just until combined. Stir in the chocolate chips and chopped hazelnuts.

Pour cookie dough into the prepared pan, smoothing the top with the spatula. Sprinkle cookie bars very lightly with sea salt. Bake cookie bars for 25-30 minutes or until the top of the bars are light golden brown and the edges start to pull away from the pan. Cool bars on a wire rack to room temperature. Cut bars into squares and serve.