Make ?Mom? lettering one day in advance. Prepare royal icing following recipe directions. Tint light rose. Use tip 3 and light rose icing, pipe ?MOM? on parchment paper-covered board. Pat smooth with finger dipped in cornstarch. Let dry overnight.
Make cake. Prepare batter following recipe directions. Bake and cool 2-layer, 3 in. high cake. Place on a foil-wrapped cake board, cut to fit.
Decorate cake. Prepare buttercream icing following recipe directions. Tint light rose. Use spatula and light rose icing to ice cake smooth. Use tip 127 and light rose icing to pipe seven rows of upside down ruffles around side of cake. To pipe an upside down ruffle, follow the ruffle instructions, but keep the narrow end lightly touching the surface and wide end facing away from surface.
Use spatula to gently remove dried ?Mom? lettering from parchment paper and place on top of cake.