Prepare the Cookie Dough: In a large mixing bowl, cream together the softened butter, caster sugar, and light brown sugar until the mixture is light and fluffy, and its colour is a pale, creamy yellow. This should take about 2-3 minutes with an electric mixer, or a good 5 minutes by hand. Scrape down the sides of the bowl to ensure everything is well combined.

Add Wet Ingredients: Beat in the large egg and vanilla extract until fully incorporated. The mixture will look smooth and glossy, with a lovely sweet fragrance of vanilla beginning to emerge.

Combine Dry Ingredients: In a separate bowl, whisk together the plain flour, bicarbonate of soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined. Be careful not to overmix; stop as soon as you no longer see streaks of flour, as the dough will appear somewhat shaggy.

Fold in Chocolate Chips: Gently fold in the chocolate chips using a spatula. The dough will be thick and studded generously with chocolate, ready for its starring role. At this point, I often sneak a tiny taste – it’s part of the baking ritual, isn't it?

Prepare the Croissants: Carefully slice each croissant lengthwise, almost all the way through, but leave one side attached so it opens like a book. You want to create a pocket without completely separating the halves. The interior will feel soft and airy, a stark contrast to the slightly crisp exterior.

Stuff the Croissants: Take a generous scoop of cookie dough – about 2-3 tablespoons per croissant, depending on its size – and gently press it into the opening of each croissant. Don't be shy; aim for a good, substantial filling. You can also press some cookie dough onto the top of the croissant. The dough should feel pliable and soft as you work it in, making the croissant feel noticeably heavier.

Bake the Crookies: Preheat your oven to 180°C (160°C fan/Gas Mark 4). Line a baking tray with parchment paper. If using, brush the tops of the stuffed croissants with the egg wash for a beautiful golden sheen. Place the crookies on the prepared baking tray, ensuring they have a little space between them.

Cook to Perfection: Bake for 15-20 minutes, or until the croissants are deeply golden brown and the cookie dough is visibly melted, bubbling slightly, and has turned a lovely golden-brown colour around the edges. You’ll smell the rich aroma of butter, chocolate, and toasted pastry filling your kitchen. The sound will be a gentle sizzle from the melting chocolate.

Cool and Serve: Once baked, carefully remove the crookies from the oven. The cookie dough will be very hot and gooey. Let them cool on the baking tray for 5-10 minutes before transferring them to a wire rack. This cooling time allows the cookie dough to set slightly, making them easier to handle without losing all that lovely molten chocolate. They're best served warm, when the chocolate is still wonderfully melted.