I want to make a cake like this:
Would you frost the blue tier on a cake board and then stack it on top? Should I frost it once it's all stacked without a cake board and then blend the blue and green in the back?
I'm not sure I would use a cake board because it is only a three tier cake at the back. I make three tier cakes often and never have any trouble with it. As for frosting I would frost the green top first, the entire top that way there is frosting between the stacked layers and the full 9" round - hope that makes sense. Then I would stack the back and then frost it on the cake along with the entire back and sides that need to be the grey/blue color. (Hope this doesn't sound like a foreign language, it made sense to me) LOL
Really nice cake idea. It will look great.
Would you frost the blue tier on a cake board and then stack it on top?
Yes. It's a 9" cake layer, cut in half and stacked to make a two-layer 9" half round cake, so you should ice it on 1/2 of a 9" cake circle.
Should I frost it once it's all stacked without a cake board and then blend the blue and green in the back?
No. The only time I'd suggest icing a cake while it's stacked on top of another is if you're trying to make a train wreck. The basic rule for stacked cakes is to use supports for every 4" of cake height, so the single-layer 9" cake on the bottom would require a support system on the half of the cake where the upper tier will be stacked. The upper tier should definitely be on its own board to prevent it from sinking down into the supports below and smashing the bottom cake.
I would use a board between the two, if for no other purpose to make it easier when it comes to serving it.
I would frost them separately.
I made one just like this, but 12" and I didn't use a board under the top layer - it was fine.
Oh - and i made the tracks go around the back and just added more trees and clouds to it.