Preheat oven to 350 degrees.
In a stand mixer, combine the room temperature butter and the brown sugar until whipped and fluffy, about 1-2 minutes.
Whisk the egg in a separate bowl, and then add to the creamed butter and sugar. In a separate small pitcher or bowl, whisk the vanilla, heavy cream and corn syrup, and then add that to the creamed butter mixture.
In a separate bowl again, mix the flour, baking soda and salt, and then slowly add to the wet ingredients, mixing minimally. Fold the chocolate chunks into the batter at the end, and dump the dough into a cast iron skillet. I reserve a few chunks of chocolate to scatter on the top.
Bake in the center rack for about 22-25 minutes, making sure not to overbake. You want a gooey underdone center, that almost needs to be spooned out of the pan. Trust me that will be the best part!
Let the cookie cake rest, until cooled, and serve topped with scoops of vanilla or cookie dough ice cream. Top with candles or sparklers, and sing Happy Birthday!