Preheat oven to 350 degrees F. Lightly coat 4 mini loaf pans with nonstick spray.
In a large bowl, combine flour, baking powder, baking soda and salt.
In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium-high until light and fluffy, about 2-3 minutes.
Beat in eggs, buttermilk and vanilla until well combined.
Beat in bananas until well combined. Gradually add flour mixture to the sugar mixture at low speed, beating just until incorporated.
Stir in blueberries and lemon zest.
Scoop the batter evenly into the loaf pans. Place into oven and bake for 30-35 minutes, or until a tester inserted in the center comes out clean.
Remove from oven and let cool for 15 minutes before inverting the loaves onto a wire rack.
Notes
Use ripe bananas. Bananas for banana bread should be ripe to overripe (heavily spotted to mostly black). The browner the banana, the sweeter, more fragrant it will be, yielding moist banana bread. Bright yellow bananas are not ideal as they will be too starchy.
Frozen blueberries can be used. Both fresh or frozen blueberries can be used in this recipe, while many prefer frozen blueberries for convenience. When using frozen blueberries, skip the thaw and add them directly from the freezer to the batter or else they will bleed. Frozen blueberries can also be coated in a little bit of all-purpose flour to suspend them in the batter and to keep them from sinking to the bottom.
Fill 2/3 full. For the best results, fill the mini loaf pans 2/3 full, allowing the batter to rise without overflowing. Overfilling the loaf pans can yield an uncooked center with crusty edges.
Serve at room temperature or warm. Banana bread is so versatile, and can be served with a morning cup of coffee or as an after school snack. Serve at room temperature or warm (lightly toasted) with a slather of butter, if desired.
Cool on a wire rack. Cooling the warm banana bread on a wire rack prevents over baking and ensures even cooling - allowing air to circulate throughout and preventing the steam from trapping at the very bottom of the loaf pan (which can yield soggy, wet banana bread loaves).
Freeze as needed. Let the banana bread cool completely on a wire rack prior to freezing to prevent sogginess and freezer burn.