Combine Dry Ingredients: In a medium bowl, whisk together the plain flour, bicarbonate of soda, and salt. Set this aside for later.

Cream Butter and Sugars: In a large bowl using a stand mixer or an electric hand mixer, beat the room temperature butter, soft light brown sugar, and granulated sugar on medium speed for about 3-4 minutes. You're looking for a light, fluffy, and pale mixture. This step incorporates air, which is key to a good cookie texture. You can learn more about the science of creaming butter and sugar from the experts.

Add Wet Ingredients: Add the egg and vanilla extract to the butter mixture and beat on low speed until just combined. Scrape down the sides of the bowl to ensure everything is evenly mixed.

Combine Wet and Dry: Pour the flour mixture into the wet ingredients. Mix on the lowest speed until the last streaks of flour have just disappeared. Be careful not to overmix here, as it can lead to tough cookies.

Fold in the Good Stuff: Gently fold in the chopped dark chocolate and the Rice Krispies with a spatula until they are evenly distributed. What works best for me is adding the cereal last to minimise breakage.

Chill the Dough: Cover the bowl with cling film and place it in the refrigerator to chill for at least 30 minutes, or up to 24 hours. This step is crucial – it solidifies the butter, which prevents the cookies from spreading into thin crisps in the oven.

Preheat and Prepare: While the dough chills, preheat your oven to 180°C (160°C fan) and line two large baking trays with parchment paper.

Scoop and Bake: Roll the chilled dough into balls, about 2 tablespoons each, and place them on the prepared baking trays, leaving about 5cm (2 inches) of space between each one to allow for spreading.

Bake to Perfection: Bake for 12-14 minutes, or until the edges are golden brown but the centres still look a little soft. They will continue to bake on the hot tray.

Cool Down: 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 up properly.