Spray a 8” cake pan with non stick spray and line with a round of parchment paper.
Make the Apple Topping:
Peel, core and cut it into quarters. Slice each quarter into very thin (1/16”) slices. Melt the butter in the microwave. In a bowl, toss the butter, brown sugar and apples together. Spread the apple mixture into a thin layer in the bottom of the prepared cake pan and bake in the oven for 10 minutes; The sugar and butter should be melted and the apples should start to soften. There may be a little liquid that has seeped out of the apples, that is fine.
Let the pan cool while you make the cake.
Make the Spice Cake:
Put the flour, baking powder, baking soda, salt, and spices in a medium bowl and whisk until blended together. In a large mixing bowl whisk the oil and sugar together, it’s actually easier to do this by hand than with an electric mixer. If you really like the mixer, use it. Add both of the eggs and whisk until smooth, you don’t have to spend a lot of time on this, just whisk it together. Add the buttermilk and vanilla and whisk until incorporated. Add the dry ingredients in two installments, whisking until blended.
Carefully pour the batter over the apple layer. If you dump it on top, you run the risk of displacing the apples and ruining the pretty apple design! (it will still taste good).
Return the pan to the oven and bake at 350 degrees for 20 to 30 minutes until the center of the cake is fully cooked. Once the cake has cooled for 20 minutes, flip it out of the cake pan and onto a cooling rack. Remove the parchment. Let cool fully while you make the frosting.
Make the Cinnamon Buttercream Frosting:
Find a pot that will fit the bottom of the bowl of a KitchenAid, fill it with three inches of water and bring to a simmer. Place the egg whites and the sugar in the mixer bowl and place over the simmering pot of water. Stir the mixture until the sugar has dissolved and the mixture is warm, about 4 minutes.
Place the bowl on the mixer fitted with the whisk attachment and beat on medium high until cool (about 8 to 10 minutes). Cut the butter into 1 inch cubes and gradually add to the mixer. Mix until the butter has incorporated and the frosting is light and fluffy (about 5 minutes). Add the salt, vanilla and cinnamon and whisk until combined.
Assemble the PieCaken:
It is easier to assemble the PieCaken if the pies are chilled.
With a small knife, cut the outer crust off the pies, leaving only the filling and the bottom crust. With a serrated knife, cut off what was the top of the cake, which is now on the bottom. Do this by cutting straight through the cake horizontally about a half inch up the side of the cake. Reserve the scraps for snacking.
On an 8 inch cake board or serving plate, place the pecan pie. Spread a ½ inch layer of frosting over the top of the pie. Place the pumpkin pie on top and spread a ½ inch of frosting on top. Place the cake, apple side up, on top of the frosting. With a serrated knife, trim the sides of the cake to be flush with the pies.
Eat the scraps.
Using an offset spatula, spread a ½ inch layer of frosting around the cake, covering the sides. Using a piping bag with whatever tip you want, pipe a pretty border around the top of the cake. I like to leave the top of the cake unfrosted so you can see the apples.
Refrigerate the PieCaken for at least an hour or tightly wrapped for up to 5 days.
Let sit at room temperature for an hour before serving so the buttercream softens.
Cut the PieCaken into 8 to 12 slices using a sharp knife dipped in hot water.