Heat oven to 350°F (175°C) and lightly grease a 4x8 inch (10x20cm) or a 5x9 inch (13x23cm) loaf pan.
Combine dry ingredients in a mixing bowl. Set aside.
Place wet ingredients in a large measuring jug and whisk to combine.
Pour wet into dry ingredients and fold with a rubber spatula JUST until dry ingredients are moistened. Do not overmix, lumps are fine.
Pour batter into prepared pan and bake for 45-55 minutes, until a toothpick inserted into the middle comes out clean.
Allow to cool in the pan for 10 minutes, then remove to a cooling rack to cook completely.
Butter: Feel free to use a neutral vegetable oil in place of the oil, if you want to make the banana bread more budget-friendly or dairy free.
Cornstarch: The cornstarch can help to make a fluffier bread, but if you don't have any on hand just replace it with the same amount of flour.
Sugar: You can make the banana bread with all granulated sugar if you don't have any light brown sugar on hand. You can also reduce the sugar for a less sweet banana bread - ½ cup is plenty for us when I make the bread for breakfast, but as a snack cake we do like the full cup.
Bananas: Make sure to use ripe bananas with brown spots. I used some bananas with brown spots and some with fully brown skin when I took the photos. It came out perfectly!
Make sure your baking powder and baking soda are not expired, this could cause them to work poorly. This would yield a dense bread that doesn't rise properly.
Do not overmix the batter. Only combine until the dry ingredients are just moistened, and always use a rubber spatula or a wooden spoon. Although I use a whisk to mix the wet and dry ingredients separately, never use a whisk to combine them into a batter. Your goal is a lumpy batter, not a smooth one! Overmixing will result in a dense and "gummy" banana bread.
Do measure your flour correctly. You want to spoon the flour into the measuring cup so the top is slightly rounded/higher than the measuring cup. Level it off with the back of a knife. You could end up with up to ½ cup too much flour if you scoop the flour directly with the measuring cup, which would result in a brick-like texture for the bread.