Preheat your oven to 350°F (175°C) and lightly grease your donut pan.

In a large bowl, whisk together the melted butter, milk, and vanilla until smooth.

Gradually mix in the sugar until dissolved and glossy.

In another bowl, combine flour, baking powder, and baking soda. Gently fold this mixture into the wet ingredients until no flour streaks remain.

Carefully fold in the blueberries without breaking them apart.

Fill each donut cavity about three-quarters full with batter.

Bake for 20-25 minutes until golden brown; check doneness using a toothpick.

Allow donuts to cool for five minutes before transferring them to a wire rack.

For glazing, whisk powdered sugar with milk and extra vanilla; dip warm donuts into the glaze.