Preheat oven to 350F. Grease and flour three 8" cake rounds and line with parchment.
In a medium bowl, whisk flour, spices, baking powder, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and until smooth. Add sugars and beat on med-high until pale and fluffy (approx 3mins).
Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture with milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Spread batter evenly between the prepared pans and smooth the tops.
Bake for approx. 40 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack to cool completely.
Apple Pie Filling:
Toss chopped apples and lemon juice in a large bowl, set aside.
In a large saucepan, combine sugars, cornstarch, and spices. Pour in water and whisk. Cook over medium heat until boiling. Cook for 2 minutes, stirring occasionally. Add apples, bring back to a boil. Simmer, stirring occasionally, until tender (10-15mins). Cool completely.
Apple Crisp Crumble:
Preheat oven to 350F. Whisk flour, oats, cinnamon, and brown sugar in a medium bowl. Add enough melted butter so that the mixture starts to clump. Spread on a parchment lined baking sheet and bake for approx. 10 mins. Cool completely. Break crumble apart if needed.
Cinnamon Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a double boiler on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch (approx. 3mins). Or registers 160F on a candy thermometer.
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.**
Add vanilla and cinnamon and whip until smooth and fluffy.
Place one layer of cake on a cake stand or serving plate. Top with approx. 1 cup of buttercream and spread evenly. Pipe a border of buttercream around the outside to hold in the apple pie filling. Fill with approx. 2/3 cup apple pie filling, spread evenly. Sprinkle with approx. 1/2 cup crumble (smaller pieces). Press gently into apple pie filling. Repeat with next layer.
Place final layer on top and do a thin crumb coat on the cake. Chill for 20mins.
Frost and smooth the top and sides of the cake with remaining frosting. Place larger chunks of the crumble around the top of the cake.
* Wipe your mixer bowl and whisk down with lemon juice or vinegar to make sure it is completely grease free and make sure there is no trace of yolk in your whites or your meringue will not stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. If it looks soupy, place it in the fridge for 20mins and rewhip.