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. Using a pastry blender or your fingertips, cut in butter until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a separate bowl, whisk together whole milk, egg, and vanilla extract until combined.
05 - Pour wet ingredients into the dry mixture. Gently mix with a spatula or wooden spoon until nearly combined—some dry streaks should remain.
06 - Add blueberries and fold gently into the dough just until distributed. 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, handling the dough as little as possible.
08 - Using a 2.5-inch round cutter, cut out biscuits with a straight downward motion. Regroup scraps gently and repeat cutting until all dough is used.
09 - Place biscuits on the prepared baking sheet, spacing them 2 inches apart. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18 to 20 minutes, or until tops are golden brown and biscuits are cooked through. Cool on baking sheet for 5 minutes before serving.