Preheat oven to 350F. Grease 3 donut pans and set aside.
In a medium bowl, whisk mashed banana, oil, sugar, egg, yogurt, buttermilk, and vanilla until smooth.
In a separate medium bowl, whisk 2 cups flour, baking soda, baking powder, and salt. Toss blueberries in separate small bowl with remaining 1 tablespoon flour. Fold flour mixture and blueberries into liquid mixture until batter is just combined.
Scrape batter into a sealable bag and seal bag. Snip a corner off of the bag and pipe batter into prepared donut pans, filling each cavity about 3/4 full.
Bake donuts at 350F 10-12 minutes until donuts spring back when lightly touched. Allow donuts to cool in pan 10 minutes then transfer to a wire cooling rack.
Vanilla Glaze
In a medium bowl, whisk powdered sugar, vanilla, and just enough milk to achieve a drizzling consistency.
Dip cooled donuts into glaze and place back on cooling rack. Allow donuts to set 10 minutes before serving. Enjoy!
Notes
Storing InstructionsStore donuts in an airtight container at room temperature up to 4 days.