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 to the flour mixture. Cut in butter using a pastry blender or fingertips until mixture resembles coarse crumbs.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until combined.
05 - Pour wet ingredients into the dry mixture. Gently mix until just barely combined—do not overmix.
06 - Gently fold blueberries into the dough until evenly distributed. Handle lightly to prevent crushing the berries.
07 - Turn dough onto a floured surface. Gently pat into a 1-inch thick rectangle without overworking.
08 - Cut out biscuits using a 2.5-inch round cutter. Regroup scraps and repeat cutting until all dough is used.
09 - Place biscuits on the prepared baking sheet. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18 to 20 minutes until golden brown on top. Cool slightly before serving.