Arrange bread cubes in a 9x13 casserole dish coated with cooking spray

In a medium bowl, mash the banana with a fork then whisk in the milk, eggs, egg whites, maple syrup, vanilla, and cinnamon until combined

Pour the mixture over the bread crumbs, coating as many as possible, tossing to coat if needed

Sprinkle the berries over the bread

Cover and chill in the refrigerator for at least 6 hours, up to overnight

When ready to bake, combine the butter and brown sugar in a bowl until it forms a paste

Remove foil from the casserole dish and put dollops of the brown sugar mixture around the casserole

Cover again and place in a cold oven

Set the temperature to 375 and bake for 35 minutes

Remove the foil and bake another 10 minutes, until golden brown