I saw a version of this cake at a bakery website in NY, Whimsical Bakehouse (whimsicalbakehouse.com). Hydrangeas are my favorite flower so I planned to make the cake at some point and thought that mother's day was a good occasion. I'm starting to realize that all my cakes turn out blue for one reason or another...hmm.
Anyhow, I used a soccer ball cake pan made by Wilton to make the round shaped cake. I only thinly iced the cake with a crumb coat and then used tip 104 for the petals. The leaf was made out of white chocolate using a leaf (it wasn't hydrangea but close enough) for a mold. The site just recommended making sure it wasn't poisonous and was washed before you used it, good advice. It wasn't terribly difficult and got good reviews from the mom and grandmothers.