Preheat your oven to 350 degrees Fahrenheit. Lightly grease a 9x13 inch baking dish with butter.

Spread your bread cubes on a baking sheet and toast for about 5 to 7 minutes. You want them to feel slightly dry to the touch, which helps them soak up the custard without turning into mush.

In a large mixing bowl, whisk together the eggs and sugars until the mixture is pale and slightly frothy. Whisk in the milk, melted butter, vanilla, cinnamon, and salt. Gently stir in the mashed bananas.

Place your toasted bread cubes into the prepared baking dish. Pour the custard mixture over the bread, ensuring every piece is submerged. Use a spatula to gently press the bread down. Let it sit for at least 20 minutes. This is the secret of how to make banana bread pudding custard perfectly.

Place the dish in the center of the oven and bake for 45 to 55 minutes. You are looking for a center that is set but still has a slight jiggle, and a top that is golden like late summer sun.

Allow the pudding to rest for 10 minutes before serving. This allows the custard to fully set and makes for easier slicing.