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.
04 - In a separate bowl, whisk together milk, egg, and vanilla extract until combined.
05 - Pour wet ingredients into the dry mixture. Gently mix with a spatula until just barely combined—do not overmix.
06 - Gently fold blueberries into the dough, being careful not to crush them or overwork the mixture.
07 - Turn dough onto a lightly 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 gently and repeat cutting until all dough is used.
09 - Place biscuits on the prepared baking sheet, leaving space between each. Sprinkle tops with coarse sugar if desired.
10 - Bake for 18–20 minutes, or until tops are golden brown and biscuits are cooked through. Cool on the baking sheet for 5 minutes before serving.