Preheat the oven to 350 degrees.
Either butter and flour or spray with baking spray a 9 by 13 inch baking dish.
In a large bowl stir together the flour, baking powder, salt and nutmeg.
In a separate bowl, or in the bowl of a stand mixer, beat together the butter and sugar until light and fluffy, about 4 – 5 minutes.
Add the vanilla to the milk in the measuring cup.
Add the eggs one at a time, mixing thoroughly after each one.
Alternate adding 1/3 of milk mixture and 1/3 of flour mixture, beating well in between.
Pour the batter into the prepared baking pan and spread evenly. Bake the cake for 30 – 35 minutes until the cake is firm and golden brown on the edges. Cool completely.
In a medium bowl, stir together the condensed milk, evaporated milk and eggnog until thoroughly blended. Poke holes all over the cooled cake.
Slowly pour one half of the eggnog mixture over the cake, then leave it for a few minutes to soak in. Pour over the remaining eggnog, cover the pan with plastic wrap and refrigerate for eight hours or overnight.
Before serving spread whipped cream or refrigerated whipped topping evenly over the top of the cake. Sprinkle lightly with nutmeg.
Cut the cake into squares and serve chilled.