For the past 9 years I have almost always used meringue buttercream for any cakes and cupcakes I've made. Today I decided to go with an American buttercream -- specifically a Mango Buttercream for some coconut cupcakes I am making tomorrow. It's an order for 300 cupcakes and I am making three different flavors, so I decided to get a head-start today. 

I used 2 1/2 sticks of butter to 5 cups powdered sugar and 3/4 cup pureed mango and a little vanilla. Well, I thought it needed a little something extra so I added two tablespoons sour cream. It's turned out a watery mess and looks broken. I looked back at the recipe and suddenly realized that I for some very odd reason doubled the mango and only the mango! Why? I have no idea!!  Now I've added a ton of powdered sugar to bring it back to a stiffer state but it just hasn't quite gotten there. 
 

Anyone have any advice on salvaging this buttercream? I really don't want to toss this entire bowl away!!

Anyone? I have added quite a bit of powdered sugar now and when in the fridge it firms up, but outside the fridge it softens quite a bit and doesn't hold a shape well at all (though it does crust). 

AI learned a long time ago from a baker that when you use butter, your sugar to butter ratio should be 4:1. So 10 ounces of butter already needs 40 ounces of sugar to keep it from breaking or separating. Keep adding sugar is all I can suggest at this point. There are so many opinions on here, you'll probably get about 6 more ideas. Good luck!

AHow much powdered sugar have you added? I'd say add more but if you've already added a LOT then maybe that isn't the fix.

I added more powdered sugar than I would like to admit!! And still, it is not as firm as it should be. So frustrating!  Not nearly my first time making buttercream so I cannot understand it ... I know I added more mango than called for, but considering how much ps I have added, I would think it should have firmed up already. Added some cornstarch a little while ago as I just read that is what some do. I will see how it looks in the morning and if it's not fixed by then, I will make the tried and true meringue buttercream --- since there are 300 cupcakes I wanted to add some variety and not top them all with some form of meringue buttercream but flavored American as well. Never would have thought the mango would prove so troublesome though!! 

I would scrap it and move on.  I only say this because it sounds to me as though you've already used enough ps to remake the entire batch.  Just start over and pay more attention to the ingredients this time.  :)  I think that would be less frustrating.  Best of luck!  I hope it turns out amazing!!!!  

AMissMona might be right. I'm crossing my fingers that it is workable in the morning for you!

AOr do a little math. If you doubled the amount of mango puree, then double up the original recipe adding to your current mixture however much butter and PS would make up a double recipe. If you've already added enough PS to throw the recipe out of whack, I would suggest you cut your losses and go with your tried-and-true.

Did you only add sugar, or did you add butter as well? If not, exactly what vgcea said.

That said, IMBC take fruit puree really well, personally I'd just scrap it and go that route, but then I get frustrated easily, haha.

It seems to me that ABC does not incorporate as much liquid as SMBC. The amount of puree you would use for your meringue buttercream may be too much for ABC.  You could make more ABC without any added liquid and then add your runny flavored buttercream until the right consistency   If you have already added more ps, maybe you just need to add butter to keep the ratio right.  Either way, the mango flavor will be diluted.  Maybe back to smbc??

Refused to give up and since I had the time, I kept at it!  The cornstarch did nothing. And though I didn't necessarily fix that broken ABC, I managed to use it to my advantage. I started a cream cheese buttercream beating some cream cheese and butter and once smooth I incorporated some of that ABC that wouldn't stiffen. It became a curdled mess!! But I did not despair, lol, just added some more butter and kept beating, for upwards of 15 minutes and it turned into a heavenly whipped buttercream. The original flavor of that mango buttercream was faint, but all's well that ends well :)

I know this is an old thread, but my answer might help others in the future with this problem. I have found that the fastest and easiest way to fix broken American Buttercream is to add a tablespoon or two (that's all it takes) of Crisco. I only had to beat mine for 30 more seconds before it was fixed.