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.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until fully combined.
05 - Pour wet ingredients into the dry mixture and gently mix until nearly combined. Do not overmix.
06 - Add blueberries and fold in gently until just distributed throughout the dough.
07 - Turn dough onto a floured surface and gently pat into a 1-inch thick rectangle.
08 - Cut out biscuits with a 2.5-inch round cutter. Regroup scraps and repeat cutting as needed.
09 - Place biscuits on prepared baking sheet. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18-20 minutes, or until golden brown. Cool slightly before serving.