Preheat oven to 400°F (200°C) and line a baking sheet with parchment. Whisk flour, sugar, baking powder, and salt, then cut in cold butter until mixture resembles coarse meal.

Stir in buttermilk and vanilla until dough starts to form, then gently fold in blueberries with a few strokes.

Pat dough into a 1-inch-thick rectangle, fold and pat twice for layers, then cut straight down with a 2.5-inch biscuit cutter without twisting.

Place biscuits on the sheet and bake 18 to 22 minutes until deep golden.

Whisk powdered sugar and lemon juice into a smooth glaze, drizzle over warm biscuits, and top with lemon zest if desired.