For browned butter: In a small saucepan, heat butter over low heat until melted. Continue heating for 10 to 12 minutes or until butter turns a delicate light brown, stirring occasionally and being careful not to burn. Remove from heat. Transfer to a small bowl. Cover and chill 2 hours or until firm.
Preheat oven to 375 degrees F. Line baking sheets with parchment paper.
In a large mixing bowl, beat chilled butter with a mixer on medium speed for 30 seconds. Add the sugars, salt, and baking soda and beat for 2 minutes or until light. Add eggs and vanilla and beat until combined. Beat in flour. Stir in the chopped white baking bar and the hazelnuts.
Using a small to medium cookie scoop, drop the dough into mounds 2 inches apart onto the prepared baking sheets. Bake for 6 to 8 minutes or until the cookies just start to brown around the edges. Remove and let cool on baking sheets for 2 minutes. Remove and cool on a wire rack.