Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with butter. Spread the cubed bread evenly in the prepared dish.
Step 2: In a large bowl, whisk together the eggs and granulated sugar until well combined and slightly pale.
Step 3: Gradually whisk in the eggnog, heavy cream, vanilla extract, cinnamon, nutmeg, cloves, and salt. If using, stir in the dark rum or brandy at this point.
Step 4: Pour the eggnog mixture evenly over the bread cubes in the baking dish. Gently press down on the bread with a spatula to ensure all the cubes are soaked in the liquid. Let it sit for 15-20 minutes to allow the bread to fully absorb the custard.
Step 5: Drizzle the melted butter over the top of the bread pudding.
Step 6: Bake for 50-60 minutes, or until the top is golden brown and a knife inserted into the center comes out mostly clean. The pudding should be set but still have a slight jiggle in the middle.
Step 7: Remove from the oven and let it cool for at least 15 minutes before serving. This allows the pudding to set properly. Serve warm with your favorite toppings like whipped cream, ice cream, or a dusting of powdered sugar.