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. Cut in butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs with some 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. Gently mix with a spatula or wooden spoon until barely combined—some dry streaks should remain.
06 - Gently fold in blueberries. Mix just until distributed without crushing the berries. Do not overmix.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle without overworking.
08 - Cut out biscuits using a 2.5-inch round cutter, pressing straight down without twisting. Gather scraps and gently re-pat to cut additional biscuits.
09 - Place biscuits on the prepared baking sheet. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18–20 minutes until golden brown on top. Cool on baking sheet for 5 minutes before serving.