Preheat oven to 350 degrees F. Spray the loaf pan (9x5 or 8x4) and line with parchment paper if you don't have just grease the pan and set aside.
In a bowl, mix butter and sugar together until light and fluffy. You can use a stand mixer or an electric mixer. If you don't have one melt butter and add sugar then mix very well. Add egg and combine.
In a small bowl, mash bananas, add vanilla and combine. Add dry ingredients together (flour, baking powder, baking soda, salt).
Toss blueberries in flour, make sure you don't burst the berries and set aside.
Sift the dry ingredients, mix all the ingredients together. (banana mixture, butter mixture, and flour) Combine until smooth, but don't overmix.
Add in the blueberries (don't burst them) into the mixture and incorporate everything.
Pour the batter into the prepared pan and bake in preheated oven for one hour until it fully cooked (insert a toothpick into the center of the bread, and it comes out clean). Allow it to cool before removing from the pan.
You can adjust the recipe to your preference.
If you try the recipe, let me know how it turns out.