Preheat oven to 350°F. Lightly grease an 8×8-inch baking dish.

Make the bananas foster sauce: In a saucepan over medium heat, melt the butter. Stir in brown sugar, vanilla, and cinnamon until bubbly. Add sliced bananas and cook 1–2 minutes, just until coated and slightly softened. Remove from heat.

Cube the sourdough bread and place evenly in the prepared baking dish.

Spoon half of the bananas foster sauce over the bread cubes.

In a bowl, whisk together milk, granulated sugar, eggs, vanilla extract, and cinnamon. Pour evenly over the bread and sauce, gently pressing bread down so it absorbs the custard.

Bake for 42–48 minutes, or until puffed, golden, and the center is set.

While still warm, spread the remaining bananas foster sauce over the top of the bread pudding.

Let cool slightly. Serve warm — fantastic with vanilla ice cream or whipped cream!