A delicious example of a buttercream cake is "Frankfurter Kranz" ("Frankfurt crown cake"). Here's an excerpt from its Wikipedia article to get an idea what it's like:

"Preparation starts with the baking of a firm sponge cake in a ring shaped baking tin. The cake is then sliced horizontally to divide it into two or three rings, and thick layers of buttercream icing are placed between the rings, usually with a layer of red jam (typically strawberry, blackcurrant or cherry jam). The outside of the cake is then thickly coated with more buttercream and topped with caramel-covered brittle nuts, called Krokant, toasted almond flakes and/or ground hazelnuts. Krokant is signature to this dish.", from https://en.wikipedia.org/wiki/Frankfurter_Kranz

Enjoy if you don't mind the calories...