Line four 7" or three 8" pans with parchment rounds and grease with non-stick baking spray.
Mix together 3 cups flour, 1 1/2 cups granulated sugar, 1 1/2 cups brown sugar, 2 1/2 tsp baking powder, 2 tsp cinnamon, 1 tsp salt, 1 tsp ginger and 1/2 tsp nutmeg in a large bowl until fully combined.
Mix 1/2 cup of unsalted butter slowly into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain.
Mix in 4 large eggs on a medium speed until just incorporated, 2 at a time.
Add 1 cup sour cream, 1/2 cup unsweetened apple sauce, 1/2 cup vegetable oil and 1 tsp of vanilla extract. Mix on a low speed until just incorporated.
Scrape down the sides of the bowl with a rubber spatula, then mix on a medium-high speed for a few more minutes to help give these cake layers structure.
Divide the batter evenly between the prepared pans and let the batter sit for about 30 minutes before baking. This helps the flour absorb moisture and prevents your cake from having a grainy texture.
As the batter sits, preheat oven to 350°F.
Bake for 32-34 minutes or until a toothpick comes out with a few moist crumbs. Allow the pans to cool for 10 minutes, then run a small offset spatula around the perimeter of the pan to separate the cake from the pan.
Flip the cake layers onto a wire rack to let them cool.
Use a serrated knife to level the tops of the layers once they're fully cooled.
If you make these cake layers in advance and freeze them, let them thaw for about 20 minutes before making your cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble your cake.