In a large bowl, whisk together the all-purpose flour, sugar, baking powder, salt, and lemon zest. Take the cold butter, cube it, and cut it into the dry ingredients.
In a medium bowl, whisk the buttermilk, vanilla, and the large egg together.
Slowly pour the wet ingredients into the dry ingredients and mix together with a silicone spatula or wooden spoon.
Once the ingredients are mixed together, add the blueberries and mix them in as best you can.
Pour the scone batter onto a floured surface and knead it for about 2 minutes until it is smooth.
Shape the dough into a circle about 8” in diameter and 1/2” thick. Using either a sharp knife or a pizza cutter, cut the dough into triangles like cutting a pizza.
Preheat your oven to 400℉/200℃/Gas Mark 6.
Place the scone slices onto a parchment-lined baking sheet. Whisk the extra egg in a small bowl and brush onto the scones. Sprinkle the tops of the scones with granulated sugar.
Bake for 22-25 minutes until they are golden-brown. Remove from the oven and let cool. Serve with fresh whipped cream, butter, or lemon icing.
To make the lemon icing, take the 1 c. of icing sugar and place it into a small bowl. Pour in the lemon juice and whisk the two ingredients together. Set aside until ready to use.