• Preheat oven to 350 F

Make the apple pie filling

• Put the apples in a saucepan, top with brown sugar and cinnamon and cook on low until the apples are soft. Add a bit of water or lemon juice if the apples are not juicy. When soft, mash the apples into a puree. Continue cooking until the juice has evaporated
  

Make the crumbs

• In a small bowl, using a fork mix together the melted butter, flour, sugar, and cinnamon until soft crumbs form.
  

Make the cake

• Grease a 9x13" pan with butter and set aside.
  
• In a large mixing bowl whisk together flour, sugar, baking powder, baking soda and salt until combined.
  
• Using a hand mixer, beat in softened butter into the flour mixture until all combined and crumbly.
  
• Add in eggs, vanilla and buttermilk and beat until fully combined, the mixture should be smooth and fluffy.
  
• Pour half of the batter into the prepared pan and spread it evenly.
  
• Sprinkle cinnamon and brown sugar.
  
• Add the apple pie filling and spread evenly.
  
• Top with the rest of the batter.
  
• Cover in a layer of crumbs
  
• Bake for about 25-30 minutes, until fully cooked. A toothpick inserted in the center of the cake should come out clean or with just a few crumbs. Cool completely before adding the glaze.

Make the glaze

• Add the powdered sugar to a medium bowl, add two tablespoons of milk and the vanilla extract.
  
• Mix until fully combined with no lumps. If the mixture is too thick add one more tablespoon of milk. The glaze should be thick but pourable.
  
• Use a fork or spoon to drizzle the icing over the cake once cooled.