Preheat oven to 425 °F (220 °C) and line a baking sheet with parchment paper; keep butter and milk cold.

In a large bowl, whisk together the flour, baking powder, sugar, and salt until even.

Cut in cold butter with a pastry cutter or your fingers until the mixture resembles coarse crumbs with small pea-sized bits remaining.

Gently fold in the blueberries so they don’t burst; if using frozen blueberries, tossing them in a bit of flour helps.

Pour in the cold milk and stir just until the dough comes together; it should be shaggy and not overworked.

Turn the dough onto a lightly floured surface, pat to about 1-inch thickness, and cut biscuits with a round cutter or glass without twisting.

Place biscuits on the prepared sheet about 1 inch apart so edges can brown evenly and bake for 12–15 minutes until tops are light golden and bottoms smell nutty.

Whisk powdered sugar, lemon juice, vanilla, and a splash of water or milk into a smooth, runny glaze; adjust as needed.

Cool biscuits briefly on a rack; while still warm, drizzle the glaze generously over them.

Let the glaze set for a minute before serving warm.