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. 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 milk, egg, and vanilla extract until fully combined.
05 - Pour wet ingredients into the dry mixture. Gently mix with a spatula or wooden spoon until just barely combined—do not overmix.
06 - Add blueberries and gently fold into the dough with 2-3 strokes. The dough should still appear slightly shaggy with visible flour streaks.
07 - Turn dough onto a lightly floured surface. Gently pat into a 1-inch thick rectangle, handling as little as possible to keep butter cold.
08 - Cut out biscuits using a 2.5-inch round cutter, pressing straight down without twisting. Gather scraps and gently pat together to cut additional biscuits.
09 - Place biscuits on the prepared baking sheet, leaving 2 inches between each. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18-20 minutes until tops are golden brown and biscuits have risen. Cool on the baking sheet for 5 minutes before serving warm.