In advance, trace 2½ in. or higher letter on paper. Tape onto a cake board and cover with waxed paper; dust with cornstarch. Tint 1 oz. fondant black; roll into log about 16-in. long. Shape fondant over letter; let dry overnight. Attach lollipop sticks to back of fondant letter with royal icing or melted candy; let dry.
Bake and cool 2-layer 6-inch round Chocolate Marble Cake. Stack cooled cake layers on foil-wrapped cake board using buttercream icing as a filling; prepare for fondant by lightly icing cake with buttercream.
Roll out white fondant, 1/16-in. thick. Cover cake with fondant; smooth.
Roll out remaining white fondant 1/8-in. thick; cut strip 3-1/2 in. (or height of cake) x 19 in. Lift fondant onto imprint mat; with rolling pin, press fondant into mat. Carefully lift fondant strip and, if necessary, re-cut to correct size. Wrap around and attach to cake sides.
Fill imprinted fondant decoration with thinned black buttercream icing and tip #2. Add tip #6 medium consistency black buttercream icing top bead border and tip #8 bead bottom border.