I normally always use IMBC, traditionally considered the more tricky buttercream to make. But today I wanted to make regular American buttercream since I want to colour it, I find IMBC hard to take deep colours. I used 6 sticks butter, 1 cup shortening which I creamed together. Then I added 1 T of vanilla before gradually adding 4 lb powdered sugar. It got quite stiff so I loosened it with 4 T milk.

I don't know what happened but it looks kind of curdled or slightly lumpy, it certainly don't look all smooth. I need to pipe with it so I want it to be smooth and creamy. I beat it on medium low for 10-15 minutes already, and the bowl is full up to the top so it is not beating in lots of air.

Anybody got an idea what is going on, and how I can rescue my BC??

OK, I really do need some ideas of what I can do. My BC is definitively curdled, it is the most bizarre thing I have ever seen. I need to finish this cake by the morning and i really don't want to be starting again at this stage. What to do??

Do I refrigerate for a bit and try again? Do I melt the whole lot and try again?