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 blended.
03 - Add cold, cubed butter to the flour mixture. Use a pastry blender or fingertips to work butter into the flour until the mixture resembles coarse crumbs with small pea-sized pieces remaining.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until combined.
05 - Pour wet ingredients into the dry mixture. Stir gently with a spatula or wooden spoon just until barely combined—some dry streaks should remain.
06 - Gently fold blueberries into the dough, taking care not to overmix to prevent purple streaking.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle, handling dough as little as possible.
08 - Use a 2.5-inch round cutter to cut out biscuits. Press straight down without twisting. Gather scraps and gently pat together to cut additional biscuits.
09 - Place biscuits on the prepared baking sheet, spacing about 2 inches apart. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18-20 minutes or until tops are golden brown. Cool on the baking sheet for 5 minutes before transferring to a wire rack.