I am making a cartoon-ish cake, with fondant. I am looking for ideas on how to make the frosting top look full and bubbly like the concept picture I made.

I thought about cutting out the shape of the "frosting" and laying it on the top of the cake and where the frosting bubbles out on the side lifting the fondant and filling underneath it with buttercream.

Anyone have suggestions?

You can carve the icing on the cake. Cut away where the actual cake will go so that the icing part is the thick part then lay the cake color on then the icing color on top of it and trim away the excess icing color.

I hope that makes sense.