Stack the layers and thinly spread the white buttercream between each layer. Chill for 20 minutes.
Make a shallow indentation at the center of the chilled 9-inch stack. Insert dowels all around the indentation.
Seal with a thin cake round, then cover the cavity with tinted buttercream.
Stack the six-inch chocolate cakes to create a tiered cake. Place full dowels through each tier.
Crumb-coat with white buttercream, chill 15 minutes.
Using petal and star tips, pipe floral buttercream on the sides.
Chill until firm, then transport upright.