I made 2 round cakes and covered them with a thin layer of butter icing for this hamburger cake. For the bottom bun I placed one cake butter icing side down onto the brown fondant icing which I wrapped partially over the top of the cake. I then spread some butter icing on it.
The “burger” is made of marzipan which I crumbled and colored at the same time with dark brown paste food coloring (wear gloves!) and then placed “leaves” made of green fondant icing on top of that, letting them hang over the edge a bit. The leaves I made by tearing pieces to give them a lettucy look, and marked veins on these. The “cheese” is a square of yellow fondant, and the “ketchup” is very thick glace icing colored red.
The top bun I made in the same way as the bottom bun and then inverted it onto the lower half of the cake. I then poked holes in it to make it look like a burger bun. It went down very well with the churchyard volunteers who do such a good job to keep it looking beautiful and for whom we hold an annual BBQ.