In a large mixing bowl, combine all dry ingredients until well combined. Set aside.
For the wet ingredients:
In a stand mixer fitted with a whisk attachment or using an electric hand mixer and large bowl, whip together bananas and sugar on high for at least 5 minutes or until fluffy.
Add in butter, eggs, and vanilla and mix until well combined and no streaks of egg remain.
To mix it and assemble:
Add flour mixture and cubed bananas to wet ingredients. MIX BY HAND just until combined. Batter may be lumpy. This is ok.
Lightly grease an 9x5 loaf pan. Pour batter into loaf pan.
Slice banana lengthwise into thin slices and arrange on top of the batter.
Bake for 1 hour to 1 hour and 15 minutes, or until toothpick inserted in the middle comes out clean.
You may want to rotate the pan in the oven if one side is browning too quickly halfway through baking.Don't be tempted to put hot butter in the batter. You'll end up with bits of scrambled eggs if you don't take the time to properly cool the butter.DO NOT OVERMIX. You can mix the dry ingredients as much as you want, and you can mix the wet ingredients as much as you want, but once they are combined, mix as little as possible or your finished product will be tough.