Preheat oven to 350ºF. Butter the bottom and sides of 6 mini cast iron skillets, or 1 (12-inch) cast iron or oven-proof skillet.
To brown the butter, add ½ cup butter (8 tablespoons or 1 stick) to a small skillet. Melt over medium heat and cook until bubbly, light to medium brown in color (not too dark) with little bits on the bottom of the pan, approximately 5-6 minutes (making sure not to burn). Cool completely.
In a medium bowl stir together brown butter and sugars until well combined. Add in egg and vanilla and stir until evenly mixed and smooth, about 3 minutes.
In a separate bowl combine flour, baking powder, baking soda, and salt and mix well. Slowly stir in dry ingredients in batches to the bowl with the wet ingredients. Add in chocolate chips and mix to combine.
Transfer the cookie batter to the prepared greased skillets and bake for 16 to 18 minutes (if using mini skillets), or 22 to 25 minutes for medium sized skillet. Bake until edges are slightly browned.
Top with vanilla ice cream and a sprinkle of espresso salt or flaky salt, if desired. Enjoy!
