Preheat the oven to 350°F. Grease and flour a 9 x 13 inch cake pan or spray with baking spray. Set aside.
Add all of the cake ingredients to a mixing bowl. Use a hand mixer and beat for 2-3 minutes until blended. Spread into the prepared pan. Bake per the directions on the package [25-30 minutes] until golden and a toothpick inserted into the center comes out clean.
While the cake is baking, in a medium saucepan, add the dry flan pudding mix and prepared eggnog. Bring to a boil, whisking constantly. Boil for 1 minute. Remove from the heat, and add the remaining ingredients. The mixture will be thin. Set into the fridge or into a bowl of ice, to cool the mixture slightly while the cake bakes.
After removing the cake from the oven, allow it to rest for 2-3 minutes on the counter. Use the end of a wooden spoon to poke holes into the cake. Carefully pour the eggnog custard evenly over the cake while it's still hot. If you've ever made a "poke" cake, it's basically the same technique.
Allow the cake to cool, then place into the refrigerator uncovered and chill completely.
After chilled, spread the whipped topping over the cake, filling the holes.
Garnish with orange curls and white chocolate. Sprinkle with nutmeg.