Preheat oven to 350°F. Spray 8 cavities in a donut pan (or pans) well with non-stick cooking spray. If using a 6-count donut pan, you will need to bake in separate batches. Set aside.
In a large mixing bowl, whisk together the flour, baking powder, and salt. Set aside.
In a separate mixing bowl, mix together the milk, sugar, egg, butter, lemon juice, lemon zest, and vanilla until fully combined. Add the dry ingredients to the wet ingredients and mix until just combined, making sure not to over mix the batter. Gently fold the blueberries into the batter.
Evenly distribute the batter between all 8 cavities of the prepared donut pan (a piping bag or spoon works well).
Bake at 350°F for 9-10 minutes or until a toothpick inserted into the donut comes out clean. Remove from the oven and allow to cool for about 10 minutes, then invert onto a wire rack to cool.