Preheat your oven to 350°F (175°C). Grease the 9x13 inch baking pan.
In a large mixing bowl, combine the flour, sugar, baking powder, and salt. Mix well.
Add the softened butter, eggs, eggnog, vanilla extract, and ground nutmeg to the dry ingredients. Using an electric mixer, beat on medium speed for about 2 minutes until the mixture is smooth and well combined.
Pour the batter into the prepared baking pan, spreading it evenly. Bake in the preheated oven for 30 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 10 minutes. Use a wooden skewer or fork to poke holes all over the top of the cake, about 1 inch apart.
Pour extra eggnog (about ¾ cup) over the top of the poked cake, allowing it to soak into the holes. Cover the cake with plastic wrap and refrigerate for at least 2 hours, or overnight for best results.
Before serving, spread the whipped topping over the chilled cake and sprinkle with additional ground nutmeg for garnish.