Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan.

Make the Cake Batter: In a mixing bowl, combine the yellow cake mix, eggnog, vegetable oil, eggs, and ground nutmeg. Beat with a whisk or electric mixer until well combined and smooth.

Bake the Cake: Pour the batter into the prepared baking pan and bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for about 10 minutes.

Poke the Cake: Using the handle of a wooden spoon or a skewer, poke holes all over the cake, about an inch apart.

Prepare the Filling: In a mixing bowl, whisk together the instant vanilla pudding mix and eggnog until smooth and thickened. Pour the mixture over the cake, making sure to fill the holes. Spread evenly with a spatula. Cover and refrigerate for at least 2 hours.

Make the Whipped Topping: In a mixing bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract until stiff peaks form.

Top the Cake: Spread the whipped cream evenly over the chilled cake. Sprinkle with ground nutmeg for garnish.

Serve and Enjoy: Cut the cake into squares and serve chilled.