Preheat oven to 350°F (175°C). Butter a 9x13-inch baking dish and set aside. If your bread is fresh, spread cubes on a baking sheet and toast at 250°F for 15 minutes until slightly dried.

In a large skillet over medium heat, melt the butter. Add brown sugar and stir until dissolved, about 1 minute. Add banana slices and cook for 3-4 minutes, flipping once, until caramelized and golden on the edges. Remove from heat.

In a large mixing bowl, whisk together eggs, milk, heavy cream, granulated sugar, vanilla extract, cinnamon, and salt until smooth and fully combined.

Place half the bread cubes in the prepared baking dish. Layer the caramelized bananas over the bread, drizzle with 1/2 cup caramel sauce, then top with remaining bread cubes.

Pour the custard mixture evenly over the bread, pressing down gently with a spatula to ensure all pieces are soaked. Let sit for 20-30 minutes at room temperature so the custard absorbs fully.

Cover the dish loosely with aluminum foil. Bake for 30 minutes, then remove foil and bake for an additional 25-30 minutes until the top is golden brown and a knife inserted in the center comes out mostly clean with just a few moist crumbs.

Let cool for 10 minutes before serving. Drizzle individual portions with the remaining caramel sauce and serve warm.