Prepare the apple layer by adding the apples and butter into a small pot over medium heat. Cook for about 5-7 minutes, stirring frequently, until the apples start to get tender.
Add in the sugar, salt, lemon, and apple pie spice. Stir well to combine.
Allow the mixture to cook for another minute to thicken the juices.
Remove from heat and allow the apple to cool.
Preheat the oven to 350 degrees
Prepare a 9-inch springform pan (or a 9-inch square pan works as well) by coating the inside with cooking spray.
Prepare the cake batter by whisking together the flour, sugar, salt, baking powder, and baking soda into a large bowl.
In a smaller bowl (I like using wet measuring cups for this so it’s easy to pour), whisk together the buttermilk, oil, egg, and vanilla.
Stir the wet ingredients into the dry ingredients with a whisk. This will be a thick batter, so once it starts to mix together switch to a spatula to make sure everything is evenly combined.
Prepare the crumble by stirring together the flour, sugars, apple pie spice, and salt together.
Stir the melted butter in with a fork until it is evenly mixed in. I like to use my hands to make sure it’s evenly mixed and the mixture sticks together if I squeeze it in my hands.
Assemble the layers together by pouring half of the cake batter into the prepared pan and use an offset spatula to spread it into an even layer.
Pour the apple mixture over the first layer of cake batter in an even layer.
Cover the apple layer with about half (or slightly less than half) of the crumble.
Cover the crumble with the rest of the cake batter. Do this by scooping little dollops of batter all around and then use an offset spatula to spread it evenly the best you can without “mixing” it with the crumble.
Pour the rest of the crumble evenly over the top of the cake layer.
Bake for about 40-45 minutes or until the center is set and a toothpick comes out clean when inserted.
Allow the cake to cool in the pan on a rack for about 15-20 minutes.
Make the icing by whisking together the powdered sugar, apple pie spice and apple cider together. You want the icing to be able to drizzle so add more cider if it’s too thick and more powdered sugar if it’s too thin.
Remove the cake from the springform pan (if using a pan that doesn’t allow for removal, then simply apply the icing onto the cake in the pan).
I like to place mine on a cake platter and drizzle the apple cider icing over liberally.
This is best served warm and fresh!