Preheat oven to 425 °F (220 °C). Line a baking sheet with parchment paper.

In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt.

Working quickly, cut cold butter into flour mixture using a pastry cutter or fingers until it resembles coarse crumbs.

Toss blueberries gently in a little flour to prevent them from sinking, then fold them into the dry mixture.

Mix together buttermilk and vanilla. Pour into flour–blueberry mix and stir until just combined—dough should be slightly shaggy and sticky.

Turn dough onto a lightly floured surface, gently pat to about 1-inch thickness.

Using a floured biscuit cutter or glass, cut out biscuits and place on the baking sheet, close but not touching.

Brush tops with a little extra buttermilk, sprinkle with coarse sugar if desired, and top each with a few reserved blueberries.

Bake 12–15 minutes, until golden on top. Let cool slightly before serving warm.