Start by creaming together the butter and sugar until light and fluffy. Then mix in the eggs on high speed until pale and creamy - just like this.
Slowly mix in the dry ingredients, then fold in the chopped dark chocolate by hand just until combined.
Spread the dough in a 10" cast iron skillet and top with extra chocolate. Bake for 25 minutes for a perfectly gooey center.
Sprinkle with sea salt when it's still warm, then let it cool for about 20 minutes before topping with your favorite ice cream.