My daughter wanted a BIG BLUE castle for her 3rd birthday in 2002. I purchased a Wilton Castle Cake Pan. Because she wanted it to stand up I baked two of the castle cakes. I made a Dunkin Hines' Golden cake and then I made a Dunkin Hines' Devil's Food cake in the castle pan. If you're baking two different kinds of cakes it may be possible to reuse your bowl and paddle/beaters without washing them if you make the white or golden cake first and then the chocolate cake. With three children I need to save as much time as I can.
After I took both of the cakes out of the pan, I put the cakes in the freezer so when I took them out they would stand better. I used the Wilton butter cream icing recipe. I always make more than I think I need because I don't like to run out while decorating cakes (yes, it has happened in the past).
I cut a little bit of the cake off the bottoms of the castles so they would stand flat. I also cut some cake off the backs so I could put icing between them using flatter surfaces. While the cake was standing I filled in and smoothed the areas between the cakes. Then I used a star tip to decorate the cake and a small circle tip to outline. I made two colored roses. Some I started with blue insides and I finished them in white and the others I started with white and finished them in blue. They are just as easy as a regular rose but different and our family and friends were really impressed. I decorated both sides of the cake the same way and finished it with clear edible glitter.
We had blue candles that looked like crayons to top it off. Isabella loved her Standing Castle From Wilton Pan Cake! It might be a good idea to start with a crumb coat because looking at the picture I can see tiny spots that I missed, with a crumb coat it wouldn't be so obvious.