• Before you start making the cookie dough, add the dried blueberries, lemon zest and lemon juice to a bowl. Stir to combine and leave to sit while you get the other ingredients organised.
• To a medium sized mixing bowl, add the melted butter, brown sugar, egg and vanilla extract. Whisk until lighter in color and texture.
• Now, add the sourdough starter to the mixture and whisk again to combine. You're looking for a light and fluffy mixture.
• To the top of this mixture, add the all purpose flour, rolled oats, baking soda, salt and the dried blueberry and lemon mixture. You might see the baking soda fizz as the lemon juice hits it.
• Mix everything together with a spatula until well combined. Cover with a plastic cover and place into the fridge for around 2 hours. You can leave the mixture to ferment for up to 24 hours if you like.
• When you're ready to bake the cookies, preheat the oven to 170C (340F). Line two cookie sheets with parchment paper and grab a cookie scoop.
• Scoop out portions of dough that weigh around 40g (I made 16 cookie dough balls weighing 40g each). Put each ball of dough onto the cookie sheet and push down a little with your fingers to flatten.
• Place the trays of sourdough blueberry cookies into the oven and bake for 15 minutes or until the edges are golden but the middle is still soft.
• Remove them from the oven and allow to cool on the tray for 10 minutes before transferring to a wire rack to fully cool.

Frosting

• To make the frosting, add the cream cheese, butter, powdered sugar and lemon juice to the bowl of a stand mixer and whisk together until light and creamy.
• Once the cookies have cooled completely, spread liberally with icing and allow a few hours for the icing to "set" before serving.