Line a large baking sheet with parchment paper and set it aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt until evenly combined.
Grate the frozen butter directly into the flour mixture using a box grater, then gently toss and work it in with your hands until the texture resembles coarse crumbs. Add the blueberries and mix lightly to distribute them evenly.
In a separate bowl, whisk together the buttermilk, egg, and vanilla extract. Pour this mixture into the dry ingredients and stir gently with a spatula until a shaggy dough forms. Use your hands to bring everything together, making sure there are no dry pockets. Adjust with a little extra flour if too sticky or a splash of buttermilk if too dry.
Transfer the dough onto a lightly floured surface and shape it into a round disk about one inch thick. Cut into eight equal wedges and place them onto the prepared baking sheet, leaving a bit of space between each piece.
Place the tray in the freezer for a short chill while the oven preheats to 400°F.
Remove the scones from the freezer, brush the tops with buttermilk, and sprinkle with coarse sugar if desired.
Bake until the tops are golden brown and the edges are set.
Transfer the scones to a wire rack and allow them to cool slightly before serving.