Preheat your oven to 350°F and grease two 6-cavity donut pans.

In a large bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon.

In a separate bowl, whisk together the buttermilk, eggs, melted butter, and vanilla.

Pour the wet ingredients into the dry and stir until just combined. Fold in the blueberries.

Transfer the batter to a piping bag and pipe into the prepared donut pans, filling each cavity ¾ full.

Bake for 8–10 minutes or until a toothpick comes out clean.

Let cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

For the glaze, whisk together powdered sugar and blueberry juice. Add milk a teaspoon at a time until smooth and dippable.

Dip the tops of the cooled donuts into the glaze and return to the wire rack to set.