Prepare Your Pan and Oven: Preheat your oven to 180°C (160°C fan/Gas Mark 4). Lightly grease a 20-23 cm (8-9 inch) oven-safe skillet or cast iron pan. The pan should be clean and have a slight sheen from the butter or oil.

Cream Butter and Sugars: In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter, light brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 2-3 minutes, and the colour will lighten to a pale, creamy yellow.

Add Egg and Vanilla: Beat in the large egg and vanilla extract until just combined. The mixture will look smooth and glossy, with no streaks of egg yolk visible.

Combine Dry Ingredients: In a separate bowl, whisk together the plain flour, bicarbonate of soda, and salt. Ensure there are no lumps, and the ingredients are evenly distributed.

Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; stop as soon as you no longer see any dry flour. The dough will be thick and shaggy, holding together when pressed.

Fold in Chocolate Chips: Gently fold in the chocolate chips by hand using a spatula until they are evenly distributed throughout the dough. The dough will now be studded with chocolate, ready for baking.

Press into Skillet: Press the cookie dough evenly into the prepared skillet. You can use your hands or the back of a spoon to ensure it reaches the edges. The surface should be relatively smooth.

Bake to Golden Perfection: Bake for 20-25 minutes, or until the edges are golden brown and set, but the centre still looks slightly soft and gooey. You'll notice a wonderful sweet, buttery aroma filling your kitchen, and the top will have a lovely crackled appearance.

Cool Slightly and Serve: Remove the skillet from the oven and let it cool on a wire rack for at least 10-15 minutes before serving. This allows the cookie to set further and the chocolate to become wonderfully molten but not scalding. A slight sizzling sound as it cools is perfectly normal.

Serve Warm: Serve warm, straight from the skillet. If you like, sprinkle with a touch of flaky sea salt to enhance the chocolate's sweetness.