01 - Preheat your oven to 400°F and line a baking sheet with parchment paper to prevent sticking.
02 - In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, salt, and lemon zest until thoroughly combined.
03 - Add the cold cubed butter to the flour mixture. Use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining.
04 - In a separate small bowl, whisk together the cold heavy cream, large egg, and vanilla extract until fully incorporated.
05 - Pour the wet mixture into the dry ingredients. Stir gently with a spatula or wooden spoon just until the dough begins to come together. Take care not to overmix, as this can result in tough scones.
06 - Gently fold in the fresh blueberries, distributing them evenly throughout the dough without crushing them.
07 - Turn the dough onto a lightly floured work surface. Gently pat it into a circle measuring 7 to 8 inches in diameter and approximately 1 inch thick.
08 - Using a sharp knife or bench scraper, cut the dough circle into 8 equal wedges. Transfer the wedges to your prepared baking sheet, leaving slight space between each scone.
09 - Lightly brush the tops of each scone with a small amount of heavy cream. Bake for 18 to 22 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.
10 - Remove from the oven and transfer the scones to a wire cooling rack. Allow them to cool completely before applying the glaze to prevent it from melting and running off.
11 - While the scones cool, whisk together the sifted powdered sugar, milk or heavy cream, and vanilla extract in a small bowl. Continue whisking until the mixture is completely smooth and has a pourable consistency.
12 - Once the scones have cooled completely, drizzle the vanilla glaze generously over each scone. Allow the glaze to set for a few minutes before serving.