A little while ago, my sister approached me with an idea. She’s doing an education degree, and her and her friends had to give a series of lessons on the geological sciences to a class of primary school kids. One of their lessons involved teaching the kids about the structure of the Earth. One of her friends came up with the idea of presenting a model of the Earth made out of cake. So my sister asked me if I could make a spherical cake with all the layers of the Earth inside it.
I told her I couldn’t do it. “How do you get a sphere inside a sphere inside a sphere?” I recall saying. “Oh yeah,” she replied, realising what it would involve.