Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper. In a large bowl, whisk together the flour, granulated sugar, baking powder, salt, and lemon zest.

Add the cold, cubed butter to the dry ingredients. Using a pastry cutter or your fingers, blend until the mixture resembles coarse crumbs. Gently fold in the blueberries, ensuring they are evenly distributed.

In a separate bowl, whisk together the buttermilk, egg, and vanilla extract. Pour the wet ingredients into the dry ingredients. Stir until just combined, being careful not to overmix.

Turn the dough out onto a lightly floured surface. Knead gently a few times until it comes together. Pat the dough into an 8-inch circle, about 1-inch thick. Using a sharp knife or a bench scraper, cut the circle into 8 equal triangles. Place the scones onto the prepared baking sheet, spacing them about 2 inches apart.

Bake for 15-20 minutes or until the scones are golden brown on the edges. Remove from the oven and let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

In a small bowl, whisk together the powdered sugar and lemon juice until smooth. Add lemon zest if desired. Once the scones are completely cool, drizzle the glaze over the top using a spoon or a piping bag.