Preheat the oven to 350 degrees F.
a 9 by 13-inch baking dish
with 1 tablespoon of the butter and set aside.
Place the cubed bread in a large mixing bowl. In a small saucepan, melt
4 tablespoons of the butter over medium heat and pour the butter over the bread cubes. Using a rubber spatula
, toss to evenly distribute the butter.
Combine the cream, milk
, eggs, brown sugar, granulated sugar, vanilla, cinnamon, nutmeg, salt, and banana liqueur
in a medium mixing bowl, whisking to combine. Pour the cream mixture over the bread cubes and stir to combine. Let sit for 30 for 45 minutes, or until the bread is soft and has absorbed most of the liquid.
Stir in the mashed bananas
and walnuts. Pour the mixture into prepared dish and bake, uncovered, for 45 to 50 minutes, until the top is golden brown and crispy and the pudding is firm in the center. Prepare the Buttery Rum Sauce while the pudding is baking.
Remove the pudding from the oven and cool on a wire rack for 15 minutes before serving. Serve warm with Buttery Rum Sauce and whipped cream, if desired.