Preheat Oven:
Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.
Mix Dry Ingredients:
In a large mixing bowl, combine the flour, granulated sugar, baking powder, and salt.
Cut in Butter:
Using a pastry cutter or fork, cut in the cold butter until the mixture resembles coarse crumbs.
Combine Wet Ingredients:
In a separate bowl, whisk together the buttermilk, egg, and vanilla extract.
Form Dough:
Add the wet ingredients to the dry ingredients and stir until just combined. Gently fold in the blueberries.
Shape Biscuits:
Turn the dough out onto a lightly floured surface and knead gently a few times. Roll out the dough to about 1/2-inch thickness. Cut into biscuits using a biscuit cutter or knife.
Bake:
Place the biscuits on the prepared baking sheet and bake for 12-15 minutes, or until golden brown.
Prepare Glaze:
While the biscuits are baking, prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract until smooth.
Glaze Biscuits:
Once the biscuits are done baking, remove them from the oven and let them cool slightly. Drizzle the glaze over the warm biscuits.