Here's my (tried and true) recipe:

6 egg whites (7 oz by weight)
10 oz sugar
1 lb unsalted butter
Vanilla to taste

I doubled the recipe, so I used 12 egg whites (never did measure how much they weighed), 1 lb 4 oz sugar, 2 lb butter, and added a generous splash of vanilla.

Whisked the egg whites and sugar over simmering water until the sugar dissolved. Transfered bowl to a stand mixer, and whipped to medium-soft peaks. Switched to the paddle, and added the butter a little bit at a time. Then I added the vanilla and continued beating. It's been beating about 10 minutes on medium speed (speed 6 on my KitchenAid) and it's still soupy.

Continue beating? Add more butter? Something else? I've used this recipe many, many times, and never had this problem.

keep beating for a little higher speed, if that doesnt work add more butter or crisco (very slowly as it can thicken up quickly) hth

Thanks. I did keep beating after I posted this. It seemed to separate, then it all came together. Cake is iced now!

I've had this problem before...it seems that often the frosting will look as if it 'curdles' before it comes back together, and we've also recently found that we have more success if the butter is cold, not room temp.