Whip butter until smooth and creamy. Add sugar and whip for 1-2 minutes until light and fluffy.
½ cup butter, ¾ cup sugar
Mix in eggs.
2 eggs
Add flour, baking powder, baking soda, cinnamon and salt. Use a silicone spatula or a heavy wooden spoon to fold flour into butter mixture. The mixture will be very thick. The flour will not be fully mixed in at this time.
2 cups flour, 1 teaspoon baking powder, 1 teaspoon baking soda, ½ teaspoon cinnamon, ¼ teaspoon salt
Fold in mashed bananas and stir until the rest of the flour is incorporated into the batter.
1½ cups mashed bananas
Fold in blueberries.
1½ cups blueberries
Pour batter into a greased 9x5 inch loaf pan.
Bake in a preheated 350°F oven for 65-75 minutes until the loaf is fully baked.
Remove from oven and cool for 10 minutes and then remove loaf from the pan. Continue cooling on a baking rack.
Notes
Use really ripe bananas. They should have lots of brown spots on the peel.
When adding the dry ingredients, add the flour, then sprinkle the baking powder, baking soda, cinnamon, and salt across the top of the flour. Then take your spoon and just lightly combine the dry ingredients. This saves from using a separate bowl.
Frozen berries may be used. Add them while still frozen. You will need to increase baking time by 10-15 minutes.
Baking time will vary depending on your oven. Test the loaf with a toothpick inserted into the center of the loaf. If there is wet batter on the toothpick, the loaf needs to bake longer.