Preheat the oven to 350 degrees Fahrenheit. Grease a 8-inch skillet or an round oven-safe baking dish.
In a large mixing bowl, cream together the softened butter, white sugar, and brown sugar until the mixture is light and fluffy.
3/4 cup softened unsalted butter, 1/3 cup white sugar, 3/4 cup light brown sugar
Add the egg, and beat. Then, and the egg yolk to the mixture, and beat well.
1 large egg, 1 egg yolk
Stir in the vanilla extract.
2 teaspoons vanilla extract
In a separate bowl, whisk together the flour, sea salt, and baking soda.
1 3/4 cup flour, 1/2 teaspoon sea salt, 1/2 teaspoon baking soda
Add the dry ingredients to the wet ingredients, mixing JUST until combined and there is no flour streaks.
Chop the dark chocolate bar into chunks.
1 8 ounce dark chocolate bar
Fold the chocolate chunks into the cookie dough.
Transfer half of the cookie dough to the greased skillet and add chocolate chips, add remaining cookie dough over the top to cover the chocolate chips, spreading it evenly.
1/2 cup chocolate chips
Bake in the preheated oven for approximately 20-25 minutes or until the edges are golden brown
Allow the cookie skillet to cool for a bit before topping with ice cream.