Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the flour, baking powder, salt, and granulated sugar. Whisk until well mixed.
Add the cold cubed butter to the dry ingredients. Using a pastry cutter or fork, mix until the mixture resembles coarse crumbs.
In a separate bowl, combine the milk and vanilla extract (if using). Gradually add the milk mixture to the flour mixture, stirring until just combined.
Gently fold in the blueberries, being careful not to break them.
Turn the dough out onto a floured surface and knead it gently 3-4 times until it holds together.
Pat the dough to about ¾ inch thick. Use a round cutter to cut out biscuits, placing them on the prepared baking sheet.
If desired, sprinkle a little extra sugar on top of the biscuits for added sweetness.
Bake in the preheated oven for 15-20 minutes or until golden brown on top.
Allow the biscuits to cool for a few minutes before serving.