Grease a 9 x 13-inch casserole dish.

Spread the cubes of bread out evenly on a baking sheet. Bake in the oven until lightly toasted, about 10 minutes.

Meanwhile, mix the diced apples, brown sugar, butter, vanilla, cinnamon, and salt to a medium saucepan.

In a large bowl, whisk together the milk, eggs, and sugar.

Bake until the liquid has set and the bread on the surface of the casserole is golden brown, about 40 minutes. When the bread pudding is done baking, a sharp knife or toothpick inserted in the center should come out clean.

While the bread pudding is baking, prepare the sauce. Combine the brown sugar and butter in a small saucepan over medium heat. Stir until the brown sugar is melted, 4 to 5 minutes.

Let sit at room temperature for 15 minutes before baking so that the bread can soak up most of the liquid.

Add the bread cubes to the prepared casserole dish. Pour the apple filling on top. Using a large spoon or rubber spatula, toss the bread chunks and apple filling together until evenly distributed. Pour the egg and milk mixture on top.

Add the heavy cream and continue to stir the mixture over heat for 1 to 2 minutes. Stir in the bourbon and let the sauce simmer for 1 minute. Remove from heat. As the sauce cools, mix it every 1 to 2 minutes to prevent the butter from separating.

Pour the sauce over the bread pudding and serve warm.