How to make a castle birthday cake

It's taken me a while to be able to write this. I can still remember the excitement tinged with fear, the screaming, the pain, the mess and the outpouring of gratitude when it was all over.
Don't worry, I'm not about to share the story of the Small Girl's birth in minute, bloody detail (though her father happily tells all and sundry the worst bits, usually at the most inappropriate times) - not when her fourth  birthday party is still fresh in my mind.
While there was a sleepless night beforehand (mine), screaming (a natural result of 10 small children being in a room with chocolate), mess (I'm sorry, rubbish collectors) and blood (the birthday girl cut her foot on something, acted like she needed amputation), it all went off without a hitch. Special thanks to my parents-in-law who are excellent cleaner-uppers in the manner of these two.
But I am taking full credit for the biggest success of the day - the castle birthday cake. Here, in response to popular demand, is how I made it.

How To Make A Castle Birthday Cake (And Survive)
I am not one of those cake decorating sort of mothers. My mother wasn't either, and since we all turned out mostly ok, I'm not too worried. When approaching this project I decided the only way to get through it was to remember it needed to suit the aesthetics of a four year old - ie, as long as it was pink, bore some resemblance to the one in the picture and there were some marshmallows lurking nearby, it would be fine. Here's how I did it:

1. The Inspiration
I found the model for this cake in More Birthday Cakes For Kids, an Australian Women's Weekly title from the library. The AWW books are birthday legends for my generation, and I must say they are rather more reliable than the AWW-branded cake tins (she says, bitterly, after the one she bought on Thursday leaked).

2. The Cake
The original recipe suggested using packet cake mix (the horror!), but I turned instead to this white chocolate mud cake recipe. It's incredibly easy - just melt and mix - and the cake can be frozen. It stays fresh for days and is firm enough for the castle construction. I used a 23cm square tin, topped with a 20cm round one. The amazing thing about the recipe I used is that it comes with a table of ingredients scaled to fit different sized tins - genius.
If time is really short, or you are not remotely a baker, a good cheat's version would be buying two sponges from the supermarket. There was a point at about 10pm on Friday when I wished I had thought of doing that earlier.

3. The Construction
The turrets are icecream cones on a base of Shrewsbury biscuits sandwiched together with icing. Warning: all the children will want one of the biscuits, so make sure you have spares (or that your husband hasn't eaten them while he is keeping you company during the building process). Make sure the cake is cold - from the fridge, when you are carving out the corners for the biscuits to sit in. Don't worry if it looks weird at this point, the icing will cover a multitude of sins.

4. The Icing
My amazing pastry chef friend gave me an incredible icing recipe, which I will share with you later in the week. Whatever you use, remember to chill the cake first (I stuck mine outside in a light southerly gale for 15 minutes) and do a light crumb coat. Resist the temptation to stab your father-in-law and husband when they mock the appearance of the cake at this point. It's a bit like seeing someone in their Spanx - it will all come together when they have their posh outfit on top.

5. Disaster Recovery
If all else fails, remember three things: marshmallows will hide any faults of construction; a neat shot of whiskey will calm your nerves and help you get to sleep and lastly, your daughter will love it.

Speaking of the daughter, it's time for me to go and whip up a birthday breakfast. What secrets of successful birthday cake baking do you have to share?