Adjust oven rack to middle position; heat oven to 425℉. Spray donut pans with a light coating of baking spray.
Combine cake flour, granulated sugar, baking powder, cinnamon and salt in a large mixing bowl. Add buttermilk, eggs, and butter, and stir until just combined. Fold in crushed blueberries.
Spoon batter into each donut cup, filling to approximately ⅔ full.
Bake at 425℉ for approximately 7-9 minutes, until golden brown. Cool in pans for 4-5 minutes before removing.
While the donuts are cooling, mix confectioners' sugar, milk, and vanilla extract together to form the glaze.
Turn the baked donuts out onto a cooling rack and drizzle with glaze.