Prepare the Pie. In a large skillet, over medium heat, combine butter and light brown sugar until combined. Add apples, lemon juice, cinnamon, nutmeg, and salt. Toss apples and coat evenly with the sugar mixture. In a small bowl, combine organic raw cane sugar and flour. Pour mixture over apples. Add vanilla. Cook over medium heat for 5-8 minutes until apples begin to soften and juices thicken.
Remove from heat and transfer apple filling to a large bowl. Allow the mixture to cool down to room temperature.
Preheat oven to 400°F. Line a 9-inch pie pan with half the pastry. Turn apple mixture into the lined pie plate. Top with remaining pastry. Trim and flute the edges. Make sure there are slits in top crust to allow steam to escape. Prepare an egg wash by mixing the egg with milk. Brush egg wash over the pie.
Bake for 35 to 40 minutes or until golden brown. Remove from oven. Allow the pie to cool at room temperature and refrigerate as you prepare the rest of the cake.
Reduce the oven temperature to 350°F. Grease and flour two 9-inch round cake pans.
Bake the Cake. Whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt. In a large bowl, beat butter and sugar at medium speed until light and fluffy, about 4 minutes. Add eggs, one at a time, and beat until well incorporated. Scrape the sides of the bowl as needed. Add applesauce and vanilla, mix until incorporated. The batter may look curdled at this stage. With the mixer at low speed, add the flour mixture and mix until just combined.
Evenly pour the batter onto the prepared pans. Bake for 23-25 minutes or until a toothpick inserted in the middle comes out clean. Remove from oven and allow the cakes to cool in the pan for 10 minutes. Remove from pans and allow cooling to room temperature.
Prepare the frosting. In a large bowl, beat the cream cheese and butter at medium speed until smooth and creamy. Reduce the speed to low and add the powdered sugar, vanilla, and spices. Return to medium speed and beat for 1 to 2 minutes, until creamy.
Assemble the cake. Evenly cut each cake layer horizontally as evenly as possible. Place 1 cake layer on a plate. Spread about ¾ cup frosting on top. Top with second layer and repeat the process. Cover with top layer. Spread the rest of the frosting over the top and sides of the cake creating a naked cake effect. Refrigerate the cake for 30 minutes or until the buttercream feels firm to the touch. Remove cake and apple pie from the refrigerator. Carefully remove the apple pie from the pan and place on top of the cake. Using a star tip, decorate the cake as desired. Add buttercream in the space between the cake and the pie for support. Sprinkle with light brown sugar on top of the frosting as decoration. Serve.
If you want to save some time, buy an organic apple pie from the store. For easier handling of the pie as you assemble the cake, consider freezing the pie beforehand. Allow enough time for the pie to defrost before serving.