In a large bowl, beat the brown sugar, white sugar, butter, and salt together until no clumps remain.
Stir in the egg and vanilla until the egg is incorporated and the mixture is very loose and resembles cake batter - about 30 seconds.
Add the flour and baking soda and mix until the dough comes together and no streaks remain - about 30 seconds.
Stir in 3/4 cup chocolate chips, reserving the remaining chocolate chips, until evenly distributed.
Scrape the batter into a 10" cast-iron skillet (or use a stainless steel skillet coated with non-stick spray). Pat the batter into the skillet with damp hands, spreading it evenly until it covers the entire bottom of the pan.
Sprinkle the remaining chocolate chips over the dough then sprinkle with sea salt.
Bake the cookie until the outer edges are browned and slightly puffed - 18-25 minutes (15-18 minutes for stainless steel).
Remove from the oven and allow to cool in the skillet for 1 hour.
When cooled, cut into wedges and serve!
Notes:
You can make this ahead and store it, but it is best served fresh and slightly warm.