Spread a thin layer of the buttercream over the entire cake to crumb coat it. (butterandbrioche.com)
Pipe a dam of buttercream on the first layer, fill in the center with a thin layer of buttercream and then top with chocolate ganache. (girlinthelittleredkitchen.com)
Top with the last layer and cover the entire cake with a thin layer of the buttercream (this is called crumb coating). (topwithcinnamon.com)