1. Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan.
2. In a large bowl, mix together mashed banana, vanilla extract, and dark chocolate chips.
3. In a separate bowl, combine flour, sugar, baking powder, and baking soda.
4. Gently mix dry ingredients into wet ingredients using a wooden spoon.
5. Lastly, add melted butter and milk, stirring until just combined.
6. Pour batter into prepared pan.
7. Bake in preheated oven for 40 minutes, or until a knife inserted into center comes out clean. Let cool before serving.