To make Salted Caramel Buttercream: In large bowl, beat shortening and butter with electric mixer on low speed until smooth. Gradually add icing sugar, 1 cup (250 mL) at a time, beating until combined; beat in vanilla. In large microwavable bowl, microwave caramels and 1 tablespoon (15 mL) of the milk uncovered on High about 1 minute or until caramels are melted; stir until smooth. Stir caramel mixture and coarse salt into buttercream mixture until combined, adding remaining milk, 1 tablespoon (15 mL) at a time, until smooth and spreadable. Frost top and side of cake with a thin layer of buttercream to make a crumb coat. Repeat, frosting the top and side of cake with a second layer of the buttercream.