Heat oven to 350°F and line a 10x15 pan with parchment paper.
Mash bananas in large bowl. Stir in sugar, butter, milk, eggs and vanilla extract and mix until combine.
Add in flour, baking powder, cinnamon, nutmeg and salt and mix until just combined. Add chocolate chips.
Spread batter evenly in pan and bake for 18-22 minutes or until a toothpick inserted in the center comes out clean. Let cool completely before cutting into squares.
Notes
Use baking powder that is less than a year old since it has been opened. If you use older baking soda, it won’t be powerful enough to help leaven the bars. You can test it by stirring half a teaspoon of baking powder into a cup of hot water. It will immediately start to fizz and release carbon dioxide gas if it’s still fresh enough to use.
If using nuts, don't skip out on roasting them. By roasting the nuts, they will stay crispy in the batter and bring out the flavor.
If you want to freeze the banana bars, place on baking sheet and freeze. Then place in ziploc bag and freeze up to 3 months and then thaw overnight in the fridge before serving.