Preheat oven to 350°F. Grease a 13x9 baking dish and line with parchment paper, if desired. Set it aside.
In a large bowl, cream together the softened butter and sugars. Beat for 1-2 minutes until light and fluffy. Add in the eggs and vanilla extract and mix to combine.
In a separate bowl, mix together the flour, baking soda, baking powder, salt, and spices. Add about half of the dry ingredients to the butter mixture, as well as half of the buttermilk. Mix until partially combined. Then, add in the rest of the dry ingredients and the rest of the buttermilk. Mix until everything is combined and your cake batter is smooth.
Pour the batter into the prepared pan. Bake for 34-36 minutes. Once done baking, the cake should be a golden color and should spring back to the touch. Allow the cake to cool completely.
To make the frosting, cream together the cream cheese and softened butter until light and fluffy. Once fluffy, add in about half of the powdered sugar, vanilla extract, and the eggnog. Mix until about halfway combined. Add in the rest of the powdered sugar and mix until combined.* Continue to beat the frosting on a medium speed for about 2 minutes. This will get the frosting light and fluffy.
Spread the frosting evenly over the cooled cake. Sprinkle with a little more cinnamon and nutmeg, and enjoy!
Notes
*If you want your frosting to be a bit thicker, add a bit more powdered sugar. If you want it more like a thinner frosting, add a splash more of eggnog.