Fit decorating bag with medium star tip. Fill bag with frosting. Starting about 1 1/2 inches from bottom edge of cake, pipe center of rosette flower, then apply steady pressure to bag while squeezing frosting, and pipe in tight circle to make flower about 2 inches in diameter. Tap tip to cake to complete flower, and lift off. Continue piping flowers to cover side of cake, staggering up and down sides so no empty spaces show. Refill piping bag as needed. Pipe rosette flowers on top of cake to cover.