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 fingertips until mixture resembles coarse crumbs with some pea-sized 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 stir with a spatula until just barely combined—some dry streaks should remain.
06 - Add blueberries and fold gently into the dough with 2-3 turns. Do not overmix to prevent tough biscuits and blueberry streaking.
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. Press straight down without twisting. Gather scraps and gently pat together to cut additional biscuits.
09 - Place biscuits on the prepared baking sheet, spacing 2 inches apart. Sprinkle tops with coarse sugar if using.
10 - Bake for 18-20 minutes until tops are golden brown and biscuits are cooked through. Cool on pan for 5 minutes before serving.