Adjust the oven rack to the upper-middle position and preheat the oven to 375 degrees.
Melt 6 tablespoons of butter in a 10-inch cast-iron skillet over medium heat.
Cook, stirring often, until the butter is dark golden brown, has a nutty aroma, and bubbling subsides, about 4-5 minutes; transfer to a large mixing bowl.
Add the remaining 2 tablespoons of butter into the hot butter and stir until completely melted.
Whisk the brown sugar, white sugar, vanilla extract, and salt into the melted butter until smooth.
Whisk in egg until smooth, about 30 seconds.
Let the mixture sit for 3 minutes then whisk for 30 seconds.
Repeat the process two more times, until the mixture is thick, smooth, and shiny. Important - don't skip this step!
Combine the flour and baking soda together until well combined.
Gradually add the flour mixture into the butter mixture until just combined, about 1 minute.
Stir in the chocolate chips, making sure no flour pockets remain.
Wipe the skillet clean with a towel.
Transfer dough to the now-empty skillet and press into an even layer with a spatula.
Place into the oven and bake for 14-16 minutes, rotating the skillet halfway through the baking time, or until the edges are golden brown and set.
Remove from the oven and place skillet directly on a cooling rack to cool for 30 minutes.
Slice cookie into wedges and serve with ice cream, if desired. Enjoy.