Preheat oven to 375, line 24 muffin pan tin with paper liners. Prepare cake mix according to pkg. directions. Stir in apples. Spoon batter into prepared muffin pans. Bake 15 to 20 minutes. Cool for 10 minutes. Prepare caramel frosting as follows: Melt butter, stir in brown sugar, evaporated milk and salt. Bring to a boil, stirring constantly. Remove from heat, cool to lukewarm. Beat in powdered sugar until frosting is of spreading consistently. Blend in vanilla.