1. Preheat oven to 350 degrees F. Grease a 13x9x2-inch baking pan; set aside. Peel, core, and coarsely shred one of the apples. Thinly slice remaining apple, removing seeds; cover and set apples aside.
2. In a large bowl whisk together the butter, brown sugar, apple butter, eggs, and vanilla until smooth. Add flour, baking powder, baking soda, and salt; whisk until combined. Fold in diced apples. Spread batter into prepared pan.
3. Bake about 30-35 minutes or until golden and a toothpick inserted near the center comes out clean. Cool on a wire rack.
4. While the cake is baking, make the icing. Combine the butter and confectioners sugar in the bowl of your stand mixer. Mix on low speed at first, then increase the speed until combined. Add in your heavy cream and vanilla extract, and mix on medium to high speed for 8 minutes until light and creamy. Stir in the caramel and final pinch of salt.
5. Using an offset spatula, ice the cooled apple cake.