Preheat oven to 325.
Butter up a 9×5-loaf pan, sprinkle with flour and set aside.
In a large mixing bowl, cream together butter and sugar and beat until smooth and creamy.
Add egg and vanilla, and continue to beat until well incorporated.
With a rubber spatula, gently fold in mashed bananas and 1/2 cup flour; set aside.
In a separate bowl, whisk together remaining flour, ground cinnamon, baking soda, baking powder, and salt.
Fold flour mixture into banana mixture until combined.
Gently fold in blueberries.
Pour batter into prepared pan.
Bake for 45 to 50 minutes, or until a toothpick inserted in the center comes out clean.
Remove from oven and let cool.
Invert onto a rack.
Cut and serve.