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 until well combined.
03 - Add cold cubed butter. Using a pastry cutter or fingertips, cut butter into dry ingredients until mixture resembles coarse crumbs.
04 - In a small bowl, whisk together milk, egg, and vanilla extract. Pour into flour mixture and stir gently until just combined.
05 - Gently fold blueberries into the dough, being careful not to overmix.
06 - Turn dough onto lightly floured surface. Pat into 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, spacing them 1 inch apart.
08 - Bake for 18-20 minutes until golden brown and cooked through.
09 - While biscuits cool slightly, mix powdered sugar, milk, and vanilla extract until smooth. Drizzle over warm biscuits before serving.