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. Use a pastry blender or your fingertips to cut in butter until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until combined.
05 - Pour the wet ingredients into the dry mixture. Stir gently with a spatula just until the dry ingredients are barely moistened. Do not overmix.
06 - Gently fold in the blueberries until evenly distributed. The dough will be slightly sticky.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle without overworking.
08 - Using a 2.5-inch round cutter, cut out biscuits and place on the prepared baking sheet. Gently regroup scraps and repeat until all dough is used.
09 - Sprinkle coarse sugar evenly over the tops of the biscuits if desired.
10 - Bake for 18-20 minutes until biscuits are golden brown on top. Cool on the baking sheet for 5 minutes before serving.