Melt the chopped dark chocolate and cubed butter over a double boiler until combined.
Whisk together the brown sugar, egg, egg yolk, and sugar until pale and fluffy.
Fold in the flour, cococa powder, salt, baking powder, and baking soda until just combined.
Scoop the dough onto a baking tray and sprinkle the top with sea salt.
Bake at 350 F for 10 minutes, cool, and enjoy!