Cookies baked in cast-iron skillets are becoming a staple to any household. Gooey, sweet, smokey, and a dash of that something special that comes with baking in cast iron. This is one of our favorite recipes — grab the mixer, your skillet, and let's get to baking!
Place a rack in lowest position in oven; preheat to 375°.
Mix brown sugar, granulated sugar, butter, and kosher salt in a large bowl until no large lumps remain, about 1 minute.
Stir in egg and vanilla until egg is incorporated and mixture is very loose and resembles cake batter, about 30 seconds. Add flour and baking soda and mix until dough comes together and no streaks remain, about 30 seconds.
Stir in ½ cup chocolate, reserving remaining chocolate, until evenly distributed.
Scrape batter into a 9" cast-iron skillet (or use a stainless steel skillet coated with nonstick vegetable oil spray). Pat batter into skillet with damp hands, pressing into an even layer so the dough extends to the sides of the pan. Scatter the remaining ½ cup of chocolate over the cookie and sprinkle with sea salt.
Bake the cookie until outer edges are browned and slightly puffed, 20–25 minutes (15–18 minutes for stainless steel). Let cool in a skillet 1 hour (if you can resist). Serve in a skillet or cut into wedges and serve with vanilla bean ice cream.