Cream the Butter and Sugars: In a large bowl, using an electric mixer or a stand mixer with the paddle attachment, beat the softened unsalted butter, caster sugar, and light brown soft sugar together on medium-high speed for about 3-4 minutes. The mixture should become light, pale, and fluffy.

Add the Wet Ingredients: Add the egg, vanilla extract, and the zest and juice of one lemon to the butter mixture. Beat again on medium speed until everything is well combined, scraping down the sides of the bowl as needed to ensure it's all incorporated.

Combine the Dry Ingredients: In a separate bowl, whisk together the plain flour, bicarbonate of soda, and salt. This ensures the raising agent and salt are evenly distributed, which helps the cookies bake uniformly.

Mix the Dough: Gradually add the dry ingredient mixture to the wet ingredients in two or three 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.

Fold in the Raspberries: Gently fold the raspberries into the cookie dough using a spatula. What works best for me is using frozen raspberries, as they hold their shape better and are less likely to break apart and bleed into the dough. If using fresh, be extra gentle.

Chill the Dough: Cover the bowl with cling film and refrigerate for at least 1 hour (or up to 3 days). This step is crucial! It solidifies the butter, which prevents the cookies from spreading into thin crisps while baking.

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

Scoop and Bake: Scoop rounded tablespoons of the chilled dough onto the prepared baking trays, leaving about 5-6cm of space between each one to allow for spreading. You should get about 24 cookies.

Bake to Perfection: Bake for 12-15 minutes, or until the edges are lightly golden brown and the centres look soft and slightly underdone. They will continue to cook on the hot tray.

Cool Completely: Leave the cookies to cool on the baking trays for 5-10 minutes before transferring them to a wire rack to cool completely. This helps them set and develop that perfect chewy texture.