In the meantime, in a large bowl, whisk together the flour, sugar, salt, baking soda, and cinnamon.
In a separate bowl, whisk together the sour cream and eggs.
Combine the wet ingredients with the dry (batter will be thick.)
Fold in the diced apples.
Gradually stir in the warm melted butter and mix well until combined.
Pour batter evenly into the prepared pan (batter will be loose.)
Carefully transfer to the oven and bake for 25-27 minutes, until the center of the cake springs back when touched. Let cool at least 30 minutes.
Make the icing by combining the butter and milk in a medium microwave safe bowl; microwave for 45 seconds, and then in 15 second intervals until butter is melted. Whisk to combine. Add in the powdered sugar, vanilla, and caramel topping; whisk to combine (add more powdered sugar or milk to get the right consistency - you want the icing to pour, but thick enough that it doesn't pool over the sides of the pan.)
Pour icing over the cake while it’s cooled, but still slightly warm. Allow to set for about 15-20 minutes.
• I chose not to peel the apples, but you can if you want! For the icing, make sure you use caramel topping, not caramel syrup, for optimal results.
• Leftovers should be covered and kept in the refrigerator for up to 5 days.