In a large bowl, cream together the room temperature butter and brown sugar using an electric hand mixer.
Mix in the lemon zest, vanilla extract and lemon juice - don't worry, it's normal for the mix to separate at this stage, it'll come back together in the next step!
In a separate small bowl, whisk together the salt, baking soda, baking powder and flour. For best results, sift them into the bowl.
Slowly add the dry ingredients into the wet ingredients. Mix until comined, then fold in the fresh blueberries with a spatula.
Place the lemon cookie dough into the fridge for 30 minutes.
Shape your cookies onto a cookie sheet using a spoon or ice cream scoop. Place the baking tray into the fridge for a minimum of 2 hours.
After 2 hrs, preheat your oven to 350°F (180°C) [320°F (160°C) fan].
Bake the cookies for 12-15 minutes or until the edges are golden brown.
Remove the tray from the oven and allow for the cookies to cool completely on a wire rack before removing them from the baking sheet.