Bird On A Cake: Hummingbird Cake with Petal Tutorial •Cover your cake with a crumb coat (very thin layer of frosting). •Prepare a decorating bag with a large round tip (Wilton #12). •Pipe a vertical line of dots on the side of your cake. •Use a small spatula to press down on each dot, dragging to the right. •Make another line of dots, just to the right of your petals. Repeat.