Preheat your oven to 375°F (190°C). Grease a donut pan with non-stick cooking spray.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, whisk together the buttermilk, egg, melted butter, and vanilla extract.
Add the wet ingredients to the dry ingredients and stir until just combined. Be careful not to overmix.
Gently fold in the blueberries until evenly distributed in the batter.
Pipe the batter evenly into the prepared donut pan, filling each mold about 2/3 full.
Bake in the preheated oven for 12-15 minutes or until the donuts are lightly golden and a toothpick inserted into the center comes out clean. Allow the donuts to cool in the pan for a few minutes, then transfer them to a wire rack to cool completely.
