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 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. Gently fold with a spatula just until the flour is nearly absorbed. Do not overmix.
06 - Gently fold blueberries into the dough until evenly distributed. Handle minimally to prevent crushing the berries or streaking the dough.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle, handling as little as possible.
08 - Using a 2.5-inch round cutter, press straight down to cut biscuits. Gather scraps gently and repeat until all dough is used.
09 - Place biscuits 2 inches apart on the prepared baking sheet. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18 to 20 minutes until tops are golden brown and biscuits are cooked through. Cool on the baking sheet for 5 minutes before transferring to a wire rack.