1. Preheat oven to 350 degrees F.

Cake:

1. Grease and dust with a bit of flour a springform pan and set aside.
2. In a large mixing bowl whisk together all-purpose flour, sugar, baking powder, baking soda, and salt until combined.
3. Using a hand mixer or a stand mixer, beat in softened butter into the flour mixture until all combined and crumbly.
4. Add in eggs, vanilla, and buttermilk and beat until fully combined, the mixture should be fluffy.
5. Pour half of the batter into the prepared pan and spread it evenly.

Cinnamon Filling:

1. In a small bowl, using a fork mix together the softened butter, flour, sugar, and cinnamon until soft crumbs form.
2. Sprinkle the mixture evenly over the cake batter. Add the remaining cake batter on top.
3. Add the apple pie filling and spread evenly. Set aside.

Apple Pie Filling:

1. You can use the homemade version by following this recipe - https://sweetandsavorymeals.com/homemade-apple-pie-filling/ , or you can use a store-bought version.

Streusel Topping:

1. In a large bowl, mix sugar with cinnamon and salt. Add in the melted butter and combine using a fork.
2. Once the butter is fully combined, add the flour little by little and mix with a fork or using your hands until fully combined and crumbs are formed.
3. Sprinkle streusel topping over the apple pie filling layer and evenly distribute.

Bake:

1. Bake cake for about 45-50 minutes, until fully cooked. A toothpick inserted in the center of the cake should come out clean or with just a few crumbs.
2. Cool completely before adding the glaze.

Glaze:

1. Add the powdered sugar to a medium bowl, add two tablespoons of milk and the vanilla extract. Mix until fully combined with no lumps.
2. If the mixture is too thick add one more tablespoon of milk. I like the glaze on the thicker side, yet pourable.
3. Use a fork or spoon to drizzle the icing over the cake.
4. Slice and serve!