I'm a big fan of Italian Meringue Buttercream. I use it for most cakes and in many flavors. For some reason it gets really soft at the best of times when I try to make a chocolate version and it is not at all heat stable. To make matters worse, the last time I made it I ended up with a very delicious chocolate soup. Nothing I did saved it, and I tried every trick I know for when I break my IMBC (which happens too often as it is). One thing I do with my IMBC is that I use less butter than a lot of recipes call for because I just prefer it that way.

My recipe:
2 cups granulated sugar (divided)

2/3 cup water

8 egg whites

dash citric acid

(for chocolate version I add 4 ounces bittersweet chocolate melted and cooled)

I mix it in the usual way for IMBC.

Does anyone have any ideas what's going wrong and how I can fix it? Would a SMBC work better with the chocolate?

Hi there! How much butter are you using in your IMBC? I use SMBC all the time and find it easy to add melted/cooled chocolate too - takes it like a dream.

My quantities are around 450g egg whites, 700g sugar, 1kg of butter

I use one pound of butter. I weigh most of my ingredients for the cake. Not sure why I don't for the buttercream. I might try using the chocolate in the SMBC. Most times I prefer the mouth feel of IMBC, but in this case it's just not working.

If you mix SMBC with Ganache it is delicious :-) 

That is good to know! I will try that for my chocolate icing.