Preheat oven to 350°F. Line four 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, 1 tsp salt, 2 tsp cinnamon, 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 low 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 beat on a low speed for a few more seconds to make sure everything is properly mixed together.

Divide the batter evenly between the prepared pans.

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 perimeter of the pan to separate the cake from the pan.

Flip the cake layers onto a wire rack to 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.

While the layers bake and cool, prepare the apple pie filling. 

Add 1/2 cup water, 1/4 cup sugar and 2 tsp of cinnamon into a large saucepan, and bring to a boil at a medium high heat.

Mix together the remaining 2 Tbsp of sugar, 2 Tbsp of water and 3 Tbsp of cornstarch to create a slurry (to thicken the filling).

Add this slurry to the saucepan and whisk continuously until the mixture thickens.

Add in 1 1/2 cups diced apples and reduce the heat to medium low. Cook for 5 minutes until the apples are partially tender (you don't want them to get too soft and turn to mush!).

Remove from heat and set aside to cool fully.

While the cake layers bake and cool, make the cinnamon cream cheese buttercream frosting.

Beat 1 cup of butter (2 sticks) and 1 cup of cream cheese on a medium speed for 30 seconds with a paddle attachment until smooth.

Mix in 1 tsp of vanilla extract, 1 tsp cinnamon and 1/2 tsp of salt.

Slowly add in 7 cups of powdered sugar, 1 cup at a time. Half way through add 2 Tbsp of heavy cream to make the frosting easier to mix.

If the frosting is too thick, add in additional cream (1 TBSP at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Stack and frost the spiced cake layers on a greaseproof cake board using a dab of frosting to help stick the first cake layer to the board.

Spread an even layer of buttercream on top of each cake layer and pipe a ring of frosting around the cake layer. Fill the center with 1/2 of the apple pie filling.

Once all the cake layers are stacked, cover the cake in a thin coat of frosting. Smooth using a bench scraper, then chill the cake in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper then decorate as desired! I colored my leftover buttercream with some gel food coloring and piped some fun swirls around the cake using an open star and small french frosting tip.