Preheat oven to 190C.
Using a stand mixer or bowl and spoon, mix brown sugar, white sugar, butter (and salt if you use it), until no large lumps remain.
Stir in egg and vanilla until egg is incorporated and mixture is smooth and runny.
Add flour and baking soda and mix until dough comes together and no flour streaks remain.
Stir in ¾ cup chocolate, reserving remaining ¼ cup of chocolate.
Scrape batter into a 25cm cast-iron oiled frying pan, or oiled stainless steel frying pan.
With damp hands, pat and press batter into an even layer extending to sides of pan.
Place remaining chocolate bits evenly over batter, sprinkle with sea salt (if using).
Bake 20–25 minutes (15–18 minutes for stainless steel) until outer edges are browned and slightly puffed.
Serve warm direct to the table with Elato vanilla ice cream (if serving it cold, wait until it cools and becomes firmer to remove from the pan.