Hello all!

I have a request for a 3D rainbow cake to feed either 20 or 25, the customer hasn't decided yet.  My plan is to bake and fill a round cake with buttercream, cut it in half and crumbcoat, then cover in fondant and decorate.  My questions are:

1.  What size would feed 20/25?  I sort of assumed I'd do a 40 serving cake & cut in half, but that would be a 10 or 12 by my standards and that seems pretty big to stand up even once cut in half.

2.  Should I just make a 10" (about 20-30 servings by my standards) and stack the whole thing on it's cut sides?  My cakes are usually about 4 inches tall.  Is 8 inches too wide?

3.  Do I need some sort of support, or will the buttercream be enough to hold the layers together?  This will be traveling about 20 minutes by car.

Thanks in advance!

I would bake sufficient batter for 20 portions, in one 10" mold. If you use 2x 8" mold (which is what I would normally use for 20 portions), when you torte, fill and cut it in half and butt one side against the other, it will be 8" wide by 4" high and 8" front to back and will look weird. In a 10" mold, with this amount of batter you won't get the full 4" height, you may only be able to torte that cake once, fill, cut in half and butt the 2 halves against each other. In theory, you should end up with an arc that is 10" wide by 5" high by 4" front to back. I think. . 

Not sure about the support thing. In theory you should get some dowels in there since it is more than 4" high at one point, however your layers are going to be vertical, not horizontal, so it's not like you will be able to pierce through all the layers with one dowel (and putting it in horizontally isn't going to do anything). I think if it was stuck down properly on the board, and your buttercream filling is a good glue, you should be OK. 

Thanks!  So I'm now thinking of baking a 10" x 3" cake, cutting it in half and stacking them together.  I would still torte it.  There will also be fondant clouds around the base, so I'm hoping that will help keep everything together.