Cut the slightly stale brioche into 1-inch cubes and spread them out on a baking sheet to dry slightly.

In a large mixing bowl, whisk the eggs until frothy then combine with warmed milk, brown sugar, cinnamon, vanilla, and salt, mixing until smooth.

Grease a baking dish and layer half of the bread cubes at the bottom, followed by banana slices and the remaining bread cubes.

Pour the custard mixture over the top, pressing down gently to ensure everything is soaked.

Cover tightly and chill in the fridge overnight.

Preheat your oven to 350°F (175°C) and let the casserole sit at room temperature for about 15 minutes before baking.

Bake uncovered for 45-50 minutes, until golden brown and set in the middle.