Preheat oven to 400 degrees. Line a 12-capacity muffin tin with baking cups.
In a medium bowl, whisk together the flour, baking powder and salt. Set aside.
In the bowl of a standing mixer, cream the butter and sugars at medium speed for 2 minutes.
Add the eggs and vanilla bean paste and continue beating for another minute.
Reduce mixer speed to low, add the flour mixture and mix until combined, scraping down the sides as needed.
Add the buttermilk and mix until incorporated. Add the mashed bananas and blueberries and mix until just combined.
Scoop the batter into the prepared muffin tins, filling each about three-quarters full. Bake for 15 minutes or until a toothpick inserted into the middle comes out clean.
Cool on a wire rack or enjoy warm!