Preheat the oven to 325F. Spray a 9×5" loaf pan with cooking oil (or two smaller loaf pans - the pan should have at least a 1" rim after it is filled)
In a bowl, mix together flour, cornstarch, baking powder, and baking soda
In another bowl, mash the ripe bananas with a fork until mostly smooth. Add in the eggs, vanilla, and salt. Mix well and set aside
In the base of a stand mixer with a paddle attachment or with a hand mixer, beat the butter and sugars until light and fluffy, around two minutes. Scrape down the sides and mix again for about 30 seconds
Add in the banana mixture and beat until incorporated. Scrape down the sides and mix again for about 30 seconds
Pour in the dry ingredients and pulse together until just combined. Mix in the chocolate chips until incorporated
Pour batter into the prepared baking pan
Bake for 75-90 minutes, or until a tester poked into the center comes out clean (depending on your oven and baking pan it may take longer or shorter, we recommend to start testing after ~1 hour) Note: if using multiple smaller pans reduce the bake time