HOT CAKE TRENDS How to make Buttercream dahlia and rose flower cake - Cake decorating tutorial by Olga Zaytseva. Learn how to make very trendy buttercream dahlia, roses and blossoms, and create this gorgeous flower cake. In variety of purple shades, this stunning floral cake perfectly suits any memorable party. Also you will learn how to layer and frost tall cake with perfectly smooth sides and create buttercream ombre effect.