Preheat the oven to 325 degrees, Prepare a 10-inch cast iron skillet with nonstick cooking spray.
In a mixing bowl, cream the butter, brown sugar, and sugar until light and creamy, about 5 minutes.
Beat in the egg and vanilla.
In a separate bowl, whisk together the flour, baking soda, and salt. Add to the mixer and beat until well mixed.
Fold in the chocolate chunks, reserving some for the top.
Transfer the batter to the prepared skillet and spread evenly. Top with the remaining chocolate chunks.
Bake for 50 to 55 minutes or until golden. Allow to rest for 10 minutes prior to serving.
Best if served warm, cut into wedges, and topped with ice cream.