In a small saucepan, add butter and melt over medium heat. Once the butter has fully melted, white foamy bubbles will begin to appear over the top of the butter. Watch carefully as the butter’s color changes to brown and the smell of the butter becomes somewhat nutty.
As soon as the butter is an amber brown color, remove from heat and cool in the refrigerator for 20-25 minutes or until it reaches room temperature.
Preheat your oven to 350 degrees and line a baking sheet with parchment paper.
In a medium sized bowl, whisk together flour, baking powder, baking soda and salt and set aside.
Pour butter into a large bowl and stir in both sugars and vanilla and thoroughly whisk until combined and continue to whip with your whisk for about 2 minutes.
Next whisk in each egg one at a time. The batter should be glossy and smooth.
Next add the flour mixture in three increments and carefully fold into the batter using a spatula until flour is completely mixed in. Pour in the Butterfinger bits and mix into the batter. Refrigerate the dough for 30-45 minutes.
Scoop out balls that are 2 tablespoon sized and add to your lined baking sheet at least 1 inch apart. Bake for 10-12 minutes.
Remove from the oven and cool for 15 minutes then serve.
To make a stiffer dough, I refrigerate for at least 30 minutes but you could definitely do up to an hour.