Melt candy bars and butter in a heavy saucepan over low heat about 5 minutes, stirring until smooth. Set aside.
Beat sugar and shortening at medium speed with an electric mixer about 3 minutes or until well blended. Add eggs, 1 at a time, beating just until blended after each addition.
Combine flour and salt. Stir together buttermilk and baking soda. Gradually add flour mixture to sugar mixture, alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in melted candy bar mixture and vanilla. Spoon batter into 3 greased and floured 9-inch cakepans.
Bake at 350° for 30 minutes or until a wooden pick comes out clean. Cool in pans on a wire rack 10 minutes; remove cakes from pans, and let cool completely on wire rack. Spread half of Chocolate-Marshmallow Frosting evenly between cake layers. Spread remaining frosting evenly over top and sides of cake. Garnish, if desired.
Note: For testing purposes only, we used Milky Way Bars.