How can I get straight sides on a filled sponge?

I was hoping that you could help with a problem that I keep having when I ice my cakes with sugar paste.

When I cover a fruit or sponge cake with sugarpaste I can get perfectly straight sides UNLESS I split the sponge and introduce a filling – normally jam or buttercream but then I get a tell tale line around the middle of the cake that is still visible as either a bulge or an indentation – no matter how careful I try to be.

Am I filling the cakes too much? Is my buttercream too soft. Should I be using something else instead of normal buttercream? After I’ve filled the middle should I be doing something else to the cake before the thin layer of buttercream and then sugarpaste?

I’d love to say scrap the filling but most people request a filling these days and although on most cakes I can hide it with decoration some I just need a lovely straight side!

Please help me to solve this problem because I have a number of Wedding Cakes later this year that simply can’t have that horrible bulge.

Many many thanks in hopeful appreciation.
Kind Regards
Sue Le Marquand

Hi Sue, There are a couple of things you can do to make your cakes smoother.

Trim the cakes a bit after filling with a super sharp knife. The cakes should be cold when doing this.

Do a preliminary coat of buttercream (crumb coat), chill the cakes and then do a thicker coat of buttercream over that, making sure that the cakes are smooth.

Roll the fondant slightly thicker than you normally do, this will give you better coverage.

Or cover your cakes first with marzipan and then the fondant or sugar paste to get a super smooth surface.

A great book with instructions on the marzipan method is in Cake Decorating: A step by step guide to making traditional and fantasy cakes. My review is on the Baking And Cake Decorating Books review page.
Hope that helps :-)