Preheat the oven to 350°F. Butter a 4×8-inch loaf pan.
In a mixing bowl, mash bananas with a fork until the texture is almost even, small clumps are fine. Pour in the melted butter and mix to combine. Add brown sugar, vanilla extract, lightly whisked eggs and yogurt. Mix to combine.
In another bowl, thoroughly mix both flours, white sugar, baking powder, baking soda, cinnamon and salt.
Pour the flour mixture into the banana mixture and gently stir until just combined. Do not over-mix.
Pour the batter into the loaf pan. Bake for about 50-60 minutes at 350°F, or until a toothpick inserted into the center comes out clean.
Let cool for 20 minutes before removing from the pan.