First, prepare the cereal. Spread the 50g of Rice Krispies on a small baking tray and toast in a preheated oven at 180°C (160°C fan) for 3-4 minutes, or until they are very lightly golden and smell nutty. Watch them carefully as they can catch quickly. Set aside to cool completely.

In a large bowl, using an electric mixer or a stand mixer with the paddle attachment, cream the softened butter, light brown sugar, and caster sugar together on medium speed for about 3-4 minutes. The mixture should become pale, light, and fluffy. This step is crucial for the cookie's texture, as explained in this great BBC Good Food guide on creaming.

Add the room temperature egg and vanilla extract to the bowl. Beat again for another minute until everything is well combined and the mixture is smooth. Scrape down the sides of the bowl to ensure everything is incorporated.

In a separate medium bowl, whisk together the plain flour, bicarbonate of soda, and fine sea salt. This ensures the raising agent and salt are evenly distributed.

Add the dry ingredients to the wet ingredients in two additions, mixing on low speed until just combined. Be careful not to overmix at this stage; stop as soon as you no longer see streaks of flour.

Gently fold in the chopped dark chocolate and the cooled, toasted Rice Krispies using a spatula. What works best for me is to use a light touch here to avoid crushing all the cereal. You want to keep that wonderful texture intact.

Cover the bowl with cling film and chill the cookie dough in the refrigerator for at least 30 minutes, or up to an hour. This step is vital—it prevents the cookies from spreading too much in the oven.

Once chilled, scoop heaped tablespoons of the dough onto baking sheets lined with parchment paper. Leave about 2 inches of space between each cookie to allow for spreading.

Bake in the preheated oven for 12-14 minutes, or until the edges are a lovely golden brown and the centres look set but are still slightly soft. They will continue to cook on the hot tray.

Let the cookies cool on the baking sheet for 5-10 minutes before transferring them to a wire rack to cool completely. This allows them to firm up so they don’t fall apart.