Preheat the oven to 350 degrees Fahrenheit and spray a 9x13x3-inch baking dish with pan spray.

Combine the vanilla cake mix, vegetable oil, 1 cup eggnog, large eggs, and ¼ teaspoon ground nutmeg in a large bowl. Beat at medium-high speed for 2 minutes using a hand mixer or stand mixer fitted with a paddle attachment.

Pour the cake batter into the prepared pan and bake for 30-35 minutes, or according to the directions on the box of the cake mix. Remove the cake from the oven and let it cool completely.

Once cooled, use the clean handle of a wooden spoon to poke holes all over the cake.

In a medium bowl, whisk together the instant vanilla pudding mix and the remaining 3 cups of eggnog until well combined and slightly thickened.

Pour the pudding mixture evenly over the cooled, poked cake, ensuring it seeps into all the holes. Refrigerate for at least 2 hours, or until the pudding is set.

Once the pudding is set, spread the thawed whipped topping evenly over the cake.

Lightly dust the top of the cake with ground cinnamon and additional ground nutmeg, if desired. Serve chilled.