Step 1: Preheat Oven and Prepare Skillet
Preheat oven to 350°F (175°C). Lightly grease a 10-inch cast iron skillet with butter or cooking spray. You can also line with parchment paper if desired, though it’s not necessary. Set aside.

Step 2: Cream Butter and Sugars
In a large mixing bowl, using an electric mixer or wooden spoon, beat the softened butter, brown sugar, and granulated sugar together until light and fluffy, about 2-3 minutes. The mixture should look creamy and slightly paler in color. This step incorporates air and creates better texture.

Step 3: Add Egg and Vanilla
Add the egg and vanilla extract to the butter mixture. Beat until fully incorporated and smooth, about 1 minute. Scrape down the sides of the bowl as needed.

Step 4: Mix Dry Ingredients
In a separate medium bowl, whisk together the flour, baking soda, and salt. This ensures even distribution of leavening and salt throughout the dough.

Step 5: Combine Wet and Dry
Add the flour mixture to the butter mixture. Using a wooden spoon or rubber spatula, mix just until combined and no flour streaks remain. Don’t overmix! The dough should be thick and slightly sticky. Fold in 1 cup of chocolate chips, distributing them evenly throughout the dough.

Step 6: Press into Skillet
Transfer the cookie dough to your prepared skillet. Using your hands or a spatula, press and spread the dough evenly across the bottom of the skillet, reaching almost to the edges. The dough will spread slightly during baking, so it doesn’t need to reach the very edge. Press the dough down firmly to eliminate air pockets. If desired, press additional chocolate chips on top for extra chocolate and beautiful presentation.

Step 7: Bake
Bake in the preheated oven for 25-30 minutes. The cookie is done when the edges are golden brown and set, but the center still looks slightly underdone and soft. It should jiggle just slightly when you gently shake the pan. Don’t overbake! The cookie continues cooking from residual heat after leaving the oven. For a 10-inch skillet, start checking at 23 minutes. For 8-inch (thicker), may need 30-33 minutes. For 12-inch (thinner), check at 20 minutes.

Step 8: Cool Slightly
Remove from oven (remember the handle is extremely hot!). Let the skillet cookie cool on a wire rack for 5-10 minutes. It will firm up as it cools but should still be warm and gooey in the center.

Step 9: Serve Immediately
Serve the skillet cookie warm, right from the skillet! Top with scoops of vanilla ice cream, drizzle with chocolate or caramel sauce if desired, and sprinkle with flaky sea salt. Provide spoons and let everyone dig in together, or cut into wedges and serve on individual plates.