Preheat and Prepare. Preheat the oven to 350°F/177°C. Spray non-stick cooking spray or grease the bottom only of a 13x9-inch pan and set aside.
Mix the Cake. To the large bowl of a large stand mixer add the cake mix, eggs, eggnog, water, oil, and nutmeg and mix on medium speed for 2 minutes.
1 Box Vanilla Cake Mix, 3 Large Eggs, ⅔ Cup Eggnog, ⅓ Cup Cold Water, ⅓ Cup Vegetable Oil, 1 Teaspoon Freshly Ground Nutmeg
Bake. Pour the batter into the prepared pan and bake for 26-28 minutes or until a toothpick or cake tester comes out clean when inserted into the center of the cake.
Cool and Poke. Allow the cake to fully cool to room temperature on a wire rack. Use the rounded end of a wooden spoon or a large straw to poke well-spaced holes into the cake.
Make Eggnog Filling. In a medium sized bowl whisk together the vanilla pudding mix, eggnog, and spiced rum.
2 Boxes Instant Vanilla Pudding Mix, 2 ½ Cups Eggnog, ½ Cup Spiced Rum
Filling the Cake. Slowly pour the pudding mixture over the cake allowing time for the pudding to fill the holes. Smooth the top of the pudding layer. Cover the cake with plastic wrap and refrigerate it for 1 hour.
Top and Garnish. Spread the whipped topping evenly over the top of the cake and sprinkle with freshly grated nutmeg. Continue to refrigerate the cake until serving time.
3 Cups Whipped Topping, Freshly Ground Nutmeg
Notes
My Top Tip♡ To give every slice lots of nice eggnog cream filling, be sure to space the holes well throughout the cake.Make it Non-Alcoholic and Family FriendlySubstitute Rum Extract. Instead of spiced rum, make the filling with 3 cups of eggnog and 2 teaspoons of rum extract.Make-Ahead & StorageMake-Ahead: You can bake the cake the day before and finish it with the filling and topping the next day.Storage: This cake must be stored in the refrigerator, covered in plastic wrap to keep it fresh tasting. Leftovers will keep up to 3 days when stored in a sealed airtight container or covered in plastic wrap.