Preheat the oven to 410 degrees F. Prep two large aluminum cookie sheets with parchment paper and set aside.
In a stand mixer fitted with a paddle attachment, whip up the butter for 1 minute until it's light and fluffy, then add in the sugars and cream together for 3 minutes on high speed.
Scrape down the sides of the bowl, and add in the vanilla and eggs one at a time. Whip up well between each addition.
Add in the cocoa, flour, cornstarch, baking soda, and salt, and slowly mix together either by hand or on the lowest mixer speed. Don't overmix!
Reserve a little bit of the add-ins, then add in the rest to the batter. Mix in on the lowest speed again until just combined. Split the dough into 8 baseball-sized balls. Place 4 balls on each cookie sheet. Hand press on the reserved add-ins, making sure to press them in firmly below the dough line. Sprinkle on some sea salt.
Bake for 9-10 minutes. They should be slightly golden, thick, tall, and gooey in the center. Let them cool on the pan for 1 minute, drizzle with the caramel, then move them onto a cooling rack to cool completely.
They will be super gooey the first day on the inside, then very soft the next day. Enjoy!