01 - In a medium saucepan, melt the butter over medium heat. Continue to cook, swirling occasionally, until butter foams and brown bits form at the bottom, about 5–7 minutes. Immediately pour into a large mixing bowl and let cool for 10 minutes.
02 - Preheat oven to 350°F (175°C). Spread hazelnuts on a baking sheet and toast for 6–8 minutes until fragrant. Let cool, then rub off skins and roughly chop.
03 - Whisk together flour, baking soda, and salt in a medium bowl.
04 - Add both sugars to the cooled brown butter. Whisk until well combined and glossy.
05 - Add eggs, one at a time, beating well after each. Stir in vanilla extract.
06 - Fold in the dry ingredients until just combined. Do not overmix.
07 - Stir in chopped hazelnuts and chocolate chips.
08 - Cover dough and chill for at least 30 minutes (optional for thicker cookies).
09 - Line baking sheets with parchment paper. Scoop dough into 2-tablespoon portions and place 2 inches apart.
10 - Bake for 11–13 minutes, until edges are golden and centers are just set.
11 - Cool on baking sheet for 5 minutes, then transfer to a wire rack to cool completely.