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 softened butter, caster sugar, and light brown sugar on medium speed for about 3-4 minutes. The mixture should become light, pale, and fluffy. This creaming method is key to a tender cookie.

Add Wet Ingredients: Add the egg and vanilla extract to the butter mixture and beat again until everything is well combined. Scrape down the sides of the bowl to ensure it's all incorporated. Then, beat in the lemon zest and fresh lemon juice.

Combine Wet and Dry: With the mixer on low speed, gradually add the dry flour mixture to the wet ingredients. Mix only until just combined – be careful not to overmix at this stage.

Fold in Blueberries: Gently fold the blueberries into the cookie dough using a spatula. If you're using frozen blueberries, add them straight from the freezer without thawing.

Chill the Dough: Cover the bowl with cling film and place it in the refrigerator to chill for at least 30 minutes. I find that an hour is even better if you have the time. This prevents the cookies from spreading too much in the oven.

Preheat and Prepare: Towards the end of the chilling time, preheat your oven to 180°C (160°C fan). Line two large baking trays with parchment paper.

Shape and Bake: Scoop out portions of dough (about 1.5 tablespoons each) and roll them into balls. 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 lightly golden but the centres still look slightly soft. They will continue to firm up as they cool.

Cool Down: Let the cookies cool on the baking trays for 5 minutes before carefully transferring them to a wire rack to cool completely.