Preheat your oven to 375° F and grease eight molds of a donut pan.
Use a mixing bowl and combine the flour, baking powder, and salt and stir together. In a separate bowl, combine the milk, egg, butter, lemon juice, zest, and vanilla extract. Mix together well and then stir the dry ingredients into the bowl of the wet ingredients until just combined, without over mixing. Use a large flat wooden spoon or rugger spatula to gently fold the blueberries into the batter.
Next, use a piping bag to carefully fill the prepared molds of the donut pan with the donut batter. Place in hot oven and bake for 10 minutes, or until a toothpick comes out clean after inserting into the center of a donut ring.
Allow to cool in the pan for 10 minutes and then invert on wire cooling rack. While the donuts are cooling, make the donut glaze recipe.
Make the Donut Glaze Recipe
Combine powdered sugar with lemon juice (or milk) in a large mixing bowl. Adjust the volume of liquid to desired consistency.
Dip the tops of the donuts in the glaze and place on a wire rack that is lined with foil underneath. Garnish with additional lemon zest and allow the glaze to set.