- Line a 13x9 pan with parchment paper and spray with a baking spray. 
- Preheat oven to 350 degrees. 
- Cream the butter with sugar in a mixing bowl with a paddle attachment. 
- Mix in egg until combined. 
- Add in sliced banana, milk, and vanilla. 
- Mix in the flour, baking powder, baking soda, and salt. 
- Stir in blueberries and chocolate chips. 
- Spread batter in the pan and bake for 30-35 minutes or until a toothpick comes out clean.