01 -
Heat the oven to 400 F. Place the butter in a 9x9-inch baking dish and set it in the oven until melted, 6-10 minutes. Remove the dish carefully.
02 -
In a large bowl, whisk the flour, sugar, baking powder, salt, and lemon zest until evenly combined.
03 -
Pour in the cold buttermilk and fold with a spatula just until a sticky dough forms and no dry flour remains.
04 -
Gently fold in 1 cup of the blueberries. Keep the strokes light so the berries do not burst and streak the dough.
05 -
Spoon the dough over the melted butter and spread it to the edges. Scatter the remaining 1/3 cup blueberries on top, then score the dough into 9 squares with a knife or spatula.
06 -
Bake for 23-27 minutes, until the top is golden, the edges are bubbling with butter, and a tester inserted into the center comes out clean. Recut along the scored lines and cool for 15-20 minutes.
07 -
Whisk the powdered sugar, lemon juice, vanilla, and salt until smooth. Drizzle over the warm biscuits and serve from the pan.