Preheat your oven to 200°C (390°F) and line a baking sheet with parchment paper.
In a large mixing bowl, whisk together the sifted flour, sugar, baking powder, and salt until well combined.
Add the cold butter cubes to the flour mixture and quickly cut them in using a pastry cutter or two forks until the mixture resembles coarse crumbs with some pea-sized pieces.
Gently fold in the lemon zest, then add the blueberries, tossing gently to distribute without breaking the berries.
In a small bowl, whisk together the buttermilk and beaten egg until combined.
Pour the wet mixture into the dry ingredients and gently fold with a spatula until just combined; the dough will be shaggy and slightly sticky.
Turn the dough onto a floured surface and gently pat it into a 2.5 cm (1-inch) thick circle. Avoid overworking the dough to keep it flaky.
Cut the circle into 8 equal triangles using a sharp knife.
Place the triangles on the prepared baking sheet, spacing them apart to allow for expansion.
Bake in the preheated oven for 15-18 minutes, until the scones are golden brown and fragrant, with crisp edges.
Remove from the oven and let cool for 5 minutes on a wire rack. Serve warm or at room temperature, enjoying the tender crumb and bright fruity flavor.