Preheat your oven to 350°F, grease your cast iron skillet with butter and set aside.
In a medium bowl, add your melted butter, granulated and dark brown sugar and whisk together.
Add egg yolk and vanilla and mix well.
Add flour, salt, and baking soda and mix into your wet ingredients using a rubber spatula.
Add your chopped chocolate or chocolate chips and stir to mix throughout.
Scrape your cookie dough into your greased skillet, and spread to the edges.
Bake your cookie for 15-18 minutes. The edges will be set and lightly browning, the center may still look slightly underdone.
Remove from oven and allow to cool for about 5-10 minutes, then add ice cream right to the center. Enjoy directly from the pan!
