01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and lemon zest.
03 - Add cold butter cubes to the dry ingredients. Use a pastry blender or fingertips to cut in the butter until the mixture resembles coarse crumbs.
04 - In a separate bowl, whisk together cold heavy cream, egg, and vanilla extract.
05 - Pour the wet ingredients into the dry mixture. Stir gently until just combined; avoid overmixing.
06 - Gently fold fresh or frozen blueberries into the dough using a spatula.
07 - Turn the dough onto a lightly floured surface. Pat into a 7-inch diameter circle about 3/4 inch thick.
08 - Cut the dough circle into 8 equal wedges and transfer them onto the prepared baking sheet.
09 - Lightly brush the tops of each wedge with heavy cream.
10 - Bake the scones for 18 to 20 minutes until they are golden brown. Remove and cool on a wire rack.
11 - Whisk together powdered sugar, milk (or cream), and vanilla extract until smooth.
12 - Drizzle the vanilla glaze over the cooled scones before serving.