01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, baking powder, and salt.
03 - Add the cold cubed butter. Using a pastry cutter or your fingertips, cut the butter into the dry ingredients until the mixture resembles coarse crumbs.
04 - In a small bowl, whisk together milk, egg, and vanilla extract. Pour into the flour mixture and stir gently until just combined—do not overmix.
05 - Gently fold in blueberries.
06 - Turn dough out onto a lightly floured surface. Pat into a 1-inch thick round. Cut out biscuits using a 2.5-inch round cutter, re-rolling scraps as needed.
07 - Place biscuits on prepared baking sheet, 1 inch apart.
08 - Bake 18-20 minutes, until golden brown and cooked through.
09 - While biscuits cool slightly, mix glaze ingredients until smooth. Drizzle over warm biscuits before serving.