Make the chocolate cake into 2 round cakes as mentioned on package directions. Cool completely. Cover and set aside.
In a mixing bowl, cream the butter, vanilla, caramel, and salt. Slowly add the powdered sugar and milk. Beat until creamy.
In another mixing bowl, cream the butter, shortening, and vanilla. Slowly add the powdered sugar, cocoa, and milk. Beat until creamy.
Spread the salted caramel butter cream on top of one round cake. Top with the other cake piece. Cover the entire cake with the chocolate butter cream and serve!
Notes
This cake can be store covered in the refrigerator for 3-4 days.