Cream the Butter and Sugars: In a large mixing bowl, using a stand mixer fitted with the paddle attachment or a hand mixer, cream together the softened unsalted butter, light brown sugar, and granulated sugar on medium speed. Beat for 3-4 minutes until the mixture is light in colour and wonderfully fluffy in texture. You'll notice a distinct change in the butter's appearance, becoming pale and aerated.

Add Eggs and Vanilla: Scrape down the sides of the bowl. Add the eggs one at a time, beating well after each addition until fully incorporated. The mixture will look glossy and smooth. Stir in the alcohol-free vanilla extract until its sweet aroma is evenly distributed throughout.

Combine Dry Ingredients: In a separate medium bowl, whisk together the plain flour, bicarbonate of soda, and fine sea salt. Ensure there are no lumps and the ingredients are thoroughly combined.

Gradually Add Dry to Wet: With the mixer on low speed, gradually add the dry ingredient mixture to the wet ingredients, mixing only until just combined. Be careful not to overmix; stop as soon as you no longer see streaks of dry flour. The dough will be thick and shaggy, a pale golden colour.

Fold in Chocolate Chunks: Remove the bowl from the mixer and, using a rubber spatula, gently fold in the milk chocolate chunks and dark chocolate chunks until evenly distributed throughout the dough. You want to see generous pockets of chocolate peeking through the rich dough.

Chill the Dough: Cover the bowl with cling film and refrigerate the dough for at least 30 minutes. This chilling time is crucial for developing flavour and preventing the cookies from spreading too much during baking. The dough will firm up and become easier to handle.

Preheat Oven and Portion Dough: While the dough chills, preheat your oven to 190°C (170°C fan/Gas Mark 5). Line a large baking tray with parchment paper. Using a large cookie scoop (approx. 60ml capacity), scoop out generous portions of dough, about 100-110g each, and place them on the prepared tray, leaving plenty of space between each cookie (I usually bake 4 cookies per standard tray). Gently press a few extra chocolate chunks onto the tops of the scooped dough balls for a beautiful finish.

Bake the Cookies: Bake for 14-18 minutes, or until the edges are lightly golden and set, but the centres still look wonderfully soft and slightly underbaked. When you open the oven, you'll be greeted by an incredible, sweet, buttery chocolate aroma. The cookies will be puffed up and golden brown around the edges, but still quite pale and soft in the middle.

Cool and Serve: Remove the tray from the oven. If desired, sprinkle a few flakes of sea salt over the warm cookies immediately. Allow the cookies to cool on the baking tray for 10-15 minutes – this is essential as they continue to cook and set. They will be too delicate to move before this time. Once slightly cooled, transfer them to a wire cooling rack to cool completely. The cookies will deepen in colour as they cool and firm up to that perfect soft-yet-chewy texture.