Begin by preheating your oven to 350°F (175°C). Prepare a 10-inch cast iron skillet by greasing it lightly with softened butter or a non-stick cooking spray to ensure easy release of the cookies later.
In a large mixing bowl, using a hand mixer or a stand mixer, cream together the softened butter, packed brown sugar, and granulated sugar on medium speed until the mixture becomes light and fluffy, about 2-3 minutes.
Add the eggs one at a time, mixing well after each addition to fully incorporate them into the batter. Then, add the pure vanilla extract and mix until combined.
In a separate bowl, whisk together the all-purpose flour, baking soda, and fine sea salt until well blended. Gradually add this dry mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; you want the dough to be soft and slightly sticky.
Gently fold in the semi-sweet chocolate chips and chopped nuts (if using) with a spatula, ensuring they are evenly dispersed throughout the cookie dough.
Transfer the cookie dough into the prepared skillet, using a spatula to spread and smooth the top evenly across the pan.
Bake in the preheated oven for 20-25 minutes. Keep an eye on it; the edges should be golden brown while the center remains soft and slightly gooey. A toothpick should come out with a few moist crumbs when inserted in the center.
Once baked, remove the skillet from the oven and allow it to cool for about 10 minutes. This makes it easier to slice into wedges.
Notes
Serve warm with vanilla ice cream and a drizzle of chocolate syrup.