With the rack in the middle position, preheat the oven to 180 °C (350 °F). Butter a 23 x 13-cm (9 x 5-inch) loaf pan.
In a bowl, combine flour, baking powder and baking soda. Set aside.
In another bowl, combine bananas with sour cream ( or yogurt). Set aside.
In a third bowl, cream butter and sugar with an electric mixer. Add egg and vanilla and beat until smooth. At low speed, add dry ingredients alternately with banana mixture.
Add the chocolate chips.
Pour into the loaf pan. Bake for about 1 hour or until a toothpick inserted in the centre of the cake comes out clean.
Let cool on a wire rack before removing from the pan and slicing.
