I want to make a cake like the three layer neopolitan rose swirl cake on iambaker...BUT want to do it as a large rectangular/sheet cake since I need a lot of servings. Anyone try that? Is there a reason it shouldn't work? Also, when I made a round rose cake before, some of the roses started falling off the sides. Also, during serving, some of the roses were separating from sides as cake was sliced. Any tips to make sure that doesn't happen? (I'd crumb coated the sides and it was dry when I piped roses. I'm thinking maybe that had to do with it?) Thanks.
I have more success with a crusting buttercream than a lighter whipping cream type. Crumb coat first. The crusting bc roses stay on no problem. As for the shape of the cake, I don't see why it should matter because it's still 3 layers, choc straw vanilla. (Trying to figure out if any way you'd cut it that would turn out wrong but I can't see how. Or maybe I haven't had enough coffee yet!)
When b'cream falls off or seperates as you describe it usually means the icing in too thick. Thin it down just a bit with some liquid. This should mean only about 2 Tablespoons liquid to about 3 or 4 cups of icing.