Preheat the oven 350°F/176°C and grease a donut pan with oil. Set aside.
In a small bowl, whisk together flour, brown sugar, salt, and baking powder.
1 cup flour, 1/2 cup brown sugar, 1 tsp baking powder, 1/4 tsp salt
In a large bowl, whisk together vanilla, sour cream, egg, and butter.
1 tbsp vanilla, 1/2 cup sour cream, 1 egg, 2 tbsp butter
Add the dry into wet and fold in gently using a spatula until no dry streaks appear. Do not over-mix!
Fold in blueberries.
1 cup fresh blueberries
Place batter in a large plastic bag and cut off about ½" from the tip. Fill donut pans. Bake for 18-20 minutes until the tops are lightly browned. You'll know it's ready when you push on the donuts and they spring back in the pan.
Slightly open the oven door and let the hot air escape for about 10 minutes. Then, remove from oven. Allow to cool completely.
Make the glaze by whisking all the ingredients together. Dip cooled donuts, and place on a cooling rack with parchment paper underneath to allow excess to drip.
1 cup powdered sugar, 1-2 tbsp milk, 1/2 tbsp vanilla
Enjoy!