Preheat oven to 350°F. Coat a loaf pan with nonstick spray or line with parchment paper.
In a bowl, combine flour, baking powder, baking soda, salt, and cinnamon.
In a large bowl or bowl of a stand mixer, cream together butter and brown sugar. Add bananas and mix, then mix in eggs.
Gradually add dry ingredients to banana mixture, mixing just until fully incorporated and no dry bits remain.
Pour batter into prepared loaf pan, spreading to the edges and corners. Bake for about 60 minutes minutes, until golden and a toothpick inserted in the center only has moist crumbs. Let cool in the pan a few minutes before removing to a wire rack to cool completely.