Zombie Barbie Cake.
Julia got a flyer in her weekly announcements envelope a month or so ago, and said, "Oh, I want to decorate a cake for the Harvest Festival competition!" The theme this year is "Monsters," so I said, "What about one of those Barbie cakes, but make her a zombie?"
I baked the cakes and assembled them, using a batch and a half of Martha Stewart's One-Bowl Chocolate Cake, with two batches of her Swiss meringue buttercream, most of that its natural color and some colored with black or brown decorating gel, and bits of torn white fondant. The flowers are done with bought frosting tubes. Julia did most of the decorating, with kibbitzing and a bit of help from me and a little more help from Laura, who couldn't resist the dripping blood.
Barbie's eyes are blanked out with white decorating gel; the blood is red gel, and the grime is cocoa powder. Her bodice is first aid gauze.
To be honest, I was tempted to title this post "How to Ruin Multiple Batches of Swiss Meringue Buttercream", but that was too depressing. The first time I made it, for Julia's first birthday, it came together absolutely perfectly, but this afternoon I made a number of stupid mistakes, exacerbated by desperation as the clock ticked away.
Here are my tips, then:
Don't rush. The sugar really does need to be fully dissolved, the meringue mixture does need to be beaten thoroughly, it does need to cool down before you start adding the butter, etc.
Make sure you've copied all the steps in the recipe. Enough said, I think.
You can warm the butter up in the microwave, but, yeah, be sure not to enter 10 minutes instead of 1. (Bangs head against microwave door.) Seriously, though, you don't want the butter too warm, or it doesn't incorporate properly. It should be softened but not warm, certainly no where near melting.
Some people use the mixer bowl for both the bain marie part and the beating part, which is certainly convenient but I suspect that this was one of my problems, and so the cough--third--time around I used a big Pyrex mixing bowl, and after the sugar was dissolved, I emptied it into the mixer bowl. I think that the stainless steel mixer bowl took too long to cool down; that's my theory, anyway, and I'm sticking with it. An added benefit to this method was that the Pyrex bowl was much wider and shallower than my KitchenAid mixer's bowl, so that the sugar dissolved more quickly and didn't get really hot.
The mixture does need to be quite cool before you start adding the butter; otherwise the butter will simply melt, and the buttercream will never set.
Be patient. It takes almost until the very last few tablespoons of butter before it starts to look like frosting instead of glop. (It actually seems to curdle at this point, and you think "oh no!" but this is absolutely right, so don't panic. Changing from the whisk to the paddle attachment smooths out the mixture wonderfully.)
If it really doesn't turn, put the mixture in the fridge for about 15 minutes, then beat a few minutes more. Try adding a few more tablespoons of butter. I'll keep my fingers crossed for you.
Rosie at Sweetapolita has done a lovely tutorial with lots of photos, very calming, and with some other advice on what you can try if it doesn't work.