Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Add the egg and vanilla extract, and mix until smooth.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the chocolate chips.
Lightly grease a 10-inch cast-iron skillet with butter or nonstick spray. Spread the cookie dough evenly into the skillet.
Bake in the preheated oven for 20-25 minutes, or until the edges are golden brown and the center is just set. For a gooey center, bake closer to 20 minutes; for a more fully cooked center, bake for 25 minutes.
Allow the skillet cookie to cool for a few minutes before serving. For an extra treat, top with a scoop of vanilla ice cream and enjoy straight from the skillet.
