Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 350°F. Meanwhile, cut 1/2 stick unsalted butter into a few pieces and place in a small microwave-safe bowl. Microwave until melted, about 20 seconds. Transfer 2 teaspoons to a 9x13-inch baking dish and brush to evenly coat the bottom and sides. Set aside the remaining melted butter.
2. Place 1 cup packed dark brown sugar then add 2 of the large bananas in a large bowl. Mash the bananas into the sugar with a fork until mostly smooth with no large chunks. Add the reserved melted butter, 1 teaspoon ground cinnamon, 1/2 teaspoon kosher salt, 1/4 to 1/2 teaspoon ground nutmeg, and 1/4 teaspoon ground ginger, if using. Mix with the fork until you have a thick paste.
3. Add 3 cups whole milk, 2 large eggs, 2 large egg yolks, 1/4 cup dark rum, and 1 teaspoon vanilla extract. Whisk until well-combined, about 1 minute.
4. Cut 1 loaf stale French bread into 1-inch cubes. Add to the banana mixture and gently fold together with a large kitchen spoon, making sure each cube is coated. Let sit until the bread has soaked up most of the custard, 5 to 7 minutes. Meanwhile, cut the remaining banana crosswise into 1/2-inch-thick rounds.
5. Pour the bread mixture into the prepared baking dish and spread into an even layer. Nestle the sliced bananas cut-side up into the mixture. Bake until the bread is puffed and golden-brown, and the bananas are slightly browned, about 1 hour. (If your baking dish is less than 4-inches deep, the butter may bubble up and over the sides of the baking dish. Place the baking dish on top of a baking sheet before baking.) Meanwhile, make the rum toffee sauce.
6. Melt 1 stick unsalted butter in a large, wide saucepan over medium heat. Add 1/2 cup packed dark brown sugar and 1/4 teaspoon kosher salt and whisk to combine. Bring to a gentle simmer, about 2 minutes. Continue cooking, whisking constantly, until it resembles caramel, 1 to 2 minutes.
7. Turn off the heat and very carefully pour in 3 tablespoons dark rum. (Be careful: The mixture will steam and bubble up.) Whisk the rum into the sugar. Bring back to a gentle simmer over medium heat. Cook, whisking frequently, until slightly darkened in color, about 1 minute.
8. Turn off the heat. Add 1/4 cup heavy cream and whisk to combine. Let sit at room temperature until ready to serve.
9. When the bread pudding is ready, let cool for 10 to 15 minutes (it will deflate slightly). Serve with the rum toffee sauce poured over each serving.