Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
In a large mixing bowl, whisk together the all-purpose flour, baking powder, sugar, and salt until well combined.
Grate or cut cold (or frozen) butter into small pieces and add it to the dry ingredients. Use a pastry cutter or your fingertips to rub in the butter until you achieve a texture resembling coarse crumbs.
Gently fold in your fresh or dried blueberries without crushing them, then pour in the cold milk and stir just until everything comes together.
Turn out your dough onto a lightly floured surface, patting it out until it reaches about an inch thick before cutting out rounds using a biscuit cutter or glass rim. Place them on your prepared baking sheet and bake for 12-15 minutes until they turn golden brown.
While your biscuits are cooling slightly, whisk together powdered sugar, water, vanilla extract, and lemon juice in a small bowl until smooth. Drizzle this glaze over warm biscuits before serving.