Preheat the oven to 400F or 210C and grease a sheet pan (16 3/4 by 12 inches) with oil or butter
Make Apple Sheet Cake
Whisk All Purpose Flour, Brown Sugar, Kosher Salt, Granulated Sugar, Baking Soda and Ground Cinnamon in a bowl.
Heat water in a saucepan over medium heat. Add the cubed butter and whisk until combined. Bring this Butter and Water mixture to a boil. As this boils, turn off the heat and take the sauce pan out. Stir in the flour mixture and fold using a rubber or wooden spatula until combined.
Pour in the Buttermilk & Vanilla Extract and stir until combined. Gently stir in the eggs, and the chopped Apples. Fold until combined.
Pour this batter in the greases sheet pan. Bake for 17-20 minutes or until a skewer inserted in the center comes out clean.
Make Salted Caramel Frosting
Here is how to make Salted Caramel from scratch. Pour this over the warm baked Apple Sheet Cake and allow it to set for 5-10 minutes before you cut it and serve