01 - Preheat your oven to 350°F. Thoroughly grease a 9x13-inch baking dish to prevent sticking.
02 - Place the prepared 1-inch French bread cubes into a large mixing bowl.
03 - In a separate bowl, whisk together the whole milk, heavy cream, large eggs, granulated sugar, vanilla extract, ground cinnamon, ground nutmeg, and salt until the mixture is completely smooth and well combined.
04 - Pour the prepared custard mixture over the bread cubes. Add the raisins, then gently fold to combine, pressing the bread down to ensure it absorbs the custard thoroughly. Allow the mixture to rest for 10 minutes to soak.
05 - Transfer the bread pudding mixture into the greased 9x13-inch baking dish. Drizzle the melted unsalted butter evenly over the top.
06 - Bake in the preheated oven for 45 to 50 minutes, or until the bread pudding is firm, golden brown on top, and a knife inserted into the center comes out clean.
07 - While the pudding bakes, begin preparing the bourbon sauce. Melt the 1/2 cup of unsalted butter in a small saucepan over low heat. Whisk in the powdered sugar until the mixture is smooth.
08 - In a small bowl, lightly beat the remaining large egg. Slowly and continuously whisk the beaten egg into the butter-sugar mixture over low heat. Continue stirring for approximately 2 to 3 minutes, or until the sauce visibly thickens.
09 - Remove the saucepan from the heat. Stir in the bourbon, or the vanilla extract if using a non-alcoholic substitute, until thoroughly combined.
10 - Serve the warm New Orleans Bread Pudding, generously drizzled with the prepared bourbon sauce over each portion.