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 evenly blended.
03 - Add cold, cubed butter. Cut into the flour mixture using a pastry blender or your fingertips until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until fully combined.
05 - Pour wet ingredients into the dry mixture. Gently fold together using a spatula until nearly combined—some dry streaks should remain.
06 - Add blueberries and fold in gently just until evenly distributed. Do not overmix to prevent tough biscuits.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle, handling the dough as little as possible.
08 - Cut out biscuits using a 2.5-inch round cutter. Press straight down without twisting. Gather scraps and gently pat together to cut additional biscuits.
09 - Place biscuits on the prepared baking sheet, leaving about 2 inches between each. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18 to 20 minutes, or until tops are golden brown and a toothpick inserted into the center comes out clean. Cool on the baking sheet for 5 minutes before serving.