• In a large bowl, combine the flour, sugar, salt and baking powder and mix it well together. Cut the cold butter into cubes and add it to the flour. Use a pastry cutter to cut the butter into small breadcrumb-sized pieces.

  Alternatively, use a food processor to cut the butter into the flour, or a cheese grater to grate the butter before adding it into the flour (then use your finger tips to rub it in, until it resembles bread crumbs.)
  
• Add in the blueberries and lemon zest and toss to combine.
  
• In a seperate bowl, whisk together the sourdough starter, egg and 3 tablespoons of the milk. Reserve the remaining tablespoon of milk.

  Make a well in the centre of the flour mixture, then pour in the sourdough mixture. Use a fork to combine it into a shaggy dough. If the mixture isn't coming together well, add in the remaining tablespoon of milk if necessary.
  
• Tip it into a clean bench and gently fold it together with your fingers until it is combined into a mound. Don’t knead the dough, or over mix it, or it will become tough. Form the dough into a circle.
  
• Use a knife or a dough scraper to cut the circle into 8 wedge pieces. Place the pieces on some baking paper and pop them into the fridge while the oven preheats. 

  If using frozen blueberries, this extra chilling step can be skipped, as the berries keep the butter cold. If skipping this step, preheat the oven while you mix the scone dough.
  
• Preheat the oven to 180°C (356°F) fan-bake, or 200°C (392°C) regular bake.

  Bake the scones in the preheated oven for around 18-20 minutes until golden brown around the edges. Once baked, leave the scones to cool before icing.
  

Lemon glaze

• In a bowl, add the lemon juice and enough icing sugar until it makes a thick but pourable glaze. Drizzle it over the cooled scones.