01 - Preheat oven to 400°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 to the flour mixture. Cut in using a pastry blender or fingertips until mixture resembles coarse crumbs.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until fully blended.
05 - Pour wet ingredients into dry mixture and gently mix until nearly combined. Add blueberries and fold in gently—do not overmix.
06 - Turn dough onto a floured surface and gently pat into a 1-inch thick rectangle. Cut out biscuits with a 2.5-inch round cutter; regroup scraps and repeat cutting as needed.
07 - Place biscuits on prepared baking sheet. Sprinkle tops with coarse sugar if desired. Bake 18-20 minutes, or until golden brown. Cool slightly before serving.