Preheat oven to 350 degrees F. Line 2 loaf pans with parchment paper.
Prepare the eggnog batter: In the bowl of your stand mixer with the paddle attachment, cream butter, sugar until fluffy about 2 minutes. Add eggs, vanilla, mayonnaise & eggnog until combined. In a separate bowl, combine flour, baking powder, pumpkin pie spice & sugar. Add dry ingredients to your batter and beat until just combined. Set aside prepared batter.
Prepare the gingerbread batter: In the bowl of your stand mixer with the paddle attachment, cream butter, sugar until fluffy about 2 minutes. Add eggs, molasses & mayonnaise until combined. In a separate bowl, combine flour, baking powder, soda & spices. Add dry ingredients to your batter and beat until just combined.
Add scoops of each batter to your prepared loaf pan, alternating between flavors to create a swirled cake. Bake for about 45-50 minutes, covering with foil at 30 minutes to avoid top from being too brown. When toothpick inserted in center comes out clean it is done.
Remove from pan and allow to cook before glazing. For the glaze combine powdered sugar and eggnog and whisk.