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