Combine Dry Ingredients: In a medium bowl, whisk together the 250g of plain flour, bicarbonate of soda, and salt. Set this aside for later.

Cream Butter and Sugars: In a large bowl using a stand mixer with the paddle attachment or a hand mixer, beat the room temperature butter, caster sugar, and light brown sugar together on medium speed for about 3-4 minutes. The mixture should become light, pale, and fluffy. This process, known as the creaming method, incorporates air into the dough, which helps the cookies rise.

Add Wet Ingredients: Add the egg, vanilla extract, lemon zest, and 1 tablespoon of lemon juice to the butter mixture. Beat on medium speed until everything is well combined, scraping down the sides of the bowl as needed to ensure it's all incorporated.

Combine Wet and Dry: Pour the dry ingredient mixture into the wet ingredients. Mix on low speed until just combined. It’s important not to overmix at this stage; stop as soon as you no longer see streaks of flour. Overmixing can lead to tough cookies.

Fold in the Blueberries: In a small, separate bowl, gently toss the fresh blueberries with the extra 1 tablespoon of flour. This light coating helps prevent them from bursting and sinking to the bottoms of the cookies. Carefully fold the flour-dusted blueberries into the cookie dough with a spatula until they are evenly distributed.

Chill the Dough: Cover the bowl with cling film and refrigerate for at least 30 minutes (or up to 2 days). I find this step is non-negotiable. It solidifies the butter, which stops the cookies from spreading into thin, crispy discs in the oven.

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 parchment paper.

Scoop and Bake: Scoop rounded tablespoons of the chilled dough onto the prepared baking trays, leaving about 5cm (2 inches) of space between each one to allow for spreading. I use a standard ice cream scoop for uniform cookies.

Bake to Perfection: Bake for 12-14 minutes, or until the edges are lightly golden brown and the centres look slightly underdone. They will continue to cook on the hot tray.

Cool Down: Let the cookies cool on the baking trays for 5 minutes before carefully transferring them to a wire rack to cool completely. They will be very soft when they first come out of the oven but will firm up as they cool.