Marzipan is type of almond paste, is very sweet and is usually wrapped around fruitcake in the UK before putting fondant over it. It is used many times for figure modeling.
You can do two layers of fondant. The marzipan is really only to give you a nice smooth neat finish to ice, as fruit cakes tend to have a uneven surface, usually and traditionally with royal icing, but with fondant you can just do two layers. If you wanted you could cover with one layer of fondant and then royal icing is also an option.
Marzipan is used on heavy fruit cakes, not on sponge. It's to cover the uneven surface of the fruit cake so that the surface icing--either royal or rolled fondant--will be smooth. Good marzipan is expensive and can be oily. Depending on the buttercream recipe, it could easily degrade it from the underside and create a deflated, weepy sponge cake.
I am just starting to do cake decorating and a recipe calls for marzipan. I can only find fondant at the craft and grocery stores. Do I have to use marzipan or can I just use fondant? What is the difference besides taste? Is there anywhere particular where I can purchase marzipan? Megan
Marzipan - Where Can I Buy It And Do I Need It? - CakeCentral.com
Marzipan is used under fondant on fruit cakes, not on standard American style cakes. Are you going to be making a lot of fruit cakes? Marzipan is not going to be the expected/accepted "icing" under fondant here in the US. Given that fondant is begrudgingly accepted by many, I can't see a resoundingly good response to fondant AND marzipan on an American cake. I know I'd be really unhappy. My ...