Bake the Cake: Preheat the oven to 350°F and grease a 9x13-inch baking pan. In a large bowl, mix together the cake mix, eggnog, water, oil, eggs, and nutmeg. Beat on medium speed for 2 minutes. Pour the batter into the prepared pan and bake for 26-28 minutes, or until a toothpick inserted into the center comes out clean.

Poke the Cake: Allow the cake to cool for about 10 minutes. Using the handle of a wooden spoon or a large straw, poke holes all over the cake.

Prepare the Filling: In a medium bowl, whisk together the pudding mix, eggnog, and spiced rum (if using) until smooth. Pour the mixture over the cake, spreading it evenly and ensuring it seeps into the holes. Cover and refrigerate for at least 4 hours.

Top the Cake: Spread the whipped topping over the chilled cake. Sprinkle with additional nutmeg for garnish.

Serve and Enjoy: Cut into squares and serve chilled. Enjoy the festive flavors!