Prepare the Oven & Skillet: Preheat the oven to 350°F. Lightly butter a 9-inch cast-iron skillet to prevent sticking.
Make the Custard: In a small pot over medium heat, combine the milk, half-and-half, brown sugar, salt, bourbon, and butter. Warm the mixture for about 3 to 4 minutes, stirring occasionally, until the butter melts and the sugar dissolves. Remove from heat and let cool slightly.
Mix the Ingredients: Once the mixture has cooled a bit, whisk in the vanilla, cinnamon, and nutmeg. Gradually add the beaten eggs, whisking continuously to ensure they don’t cook.
Soak the Bread: Place the challah cubes in the buttered cast-iron skillet, making sure they are evenly spread. Pour the custard mixture over the bread, ensuring it seeps into all the cracks. Let sit for 10-15 minutes so the bread can fully absorb the liquid.
Bake the Bread Pudding: Transfer the skillet to the oven and bake for 25-30 minutes, or until the top is golden brown and a knife inserted into the center comes out clean. The shallower depth of the skillet allows for a slightly quicker bake than a deep dish.
Prepare the Salted Caramel Sauce: While the pudding bakes, heat the sugar in a heavy-bottomed saucepan over medium heat, stirring continuously with a wooden spoon. Once the sugar melts and turns an amber color, add the butter, stirring until fully combined. If the butter starts to separate, remove from heat and whisk vigorously until smooth before returning to the stove.
Finish the Caramel Sauce: Let the caramel sit for 1 minute, then slowly add the heavy cream, stirring carefully as it may bubble up. Once all the cream is incorporated, allow the sauce to boil for 1 minute before removing it from the heat. Stir in the salt and let the sauce cool slightly.
Serve & Enjoy: Cut the bread pudding into portions and serve warm. Drizzle generously with the salted caramel sauce for an irresistible finish.