Combine Wet Ingredients: In a large bowl, or the bowl of a stand mixer fitted with the paddle attachment, whisk together the slightly cooled melted butter, soft light brown sugar, and granulated sugar. Mix on medium speed for about 2-3 minutes until well combined. The mixture will look like wet sand.

Add Eggs and Vanilla: Add the whole egg, egg yolk, and vanilla extract. Beat again for another 2 minutes until the mixture becomes lighter in colour and texture, and looks glossy.

Combine Dry Ingredients: In a separate medium bowl, whisk together the plain flour, bicarbonate of soda, baking powder, and fine sea salt. This ensures the raising agents are evenly distributed.

Mix the Dough: Gradually add the dry ingredients to the wet ingredients, mixing on a low speed until just combined. Be careful not to overmix at this stage; stop as soon as you no longer see streaks of flour. What works best for me is finishing the last few turns with a spatula to avoid a tough cookie.

Fold in the Chocolate: Gently fold in the chopped dark chocolate with a spatula until it's evenly distributed throughout the dough.

Rest the Dough: Cover the bowl with cling film and place it in the refrigerator to chill for at least 30 minutes, or up to 72 hours. This step is crucial for flavour development and prevents the cookies from spreading too much in the oven.

Preheat and Prepare: When you're ready to bake, preheat your oven to 180°C (160°C fan/Gas Mark 4). Line two large baking trays with parchment paper.

Portion the Cookies: Scoop out portions of dough using a medium ice cream scoop (about 2 tablespoons each). Roll them into balls and place them on the prepared baking trays, leaving at least 5cm (2 inches) of space between each one to allow for spreading.

Bake to Perfection: Sprinkle a little flaky sea salt over the top of each dough ball, if using. Bake for 12-15 minutes, or until the edges are golden brown but the centres still look slightly soft and underdone. They will continue to cook on the hot tray.

Cool and Enjoy: Let the cookies cool on the baking tray for 5 minutes before transferring them to a wire rack to cool completely. This helps them set properly.