rlowry - the first time I made IMBC I too found it way too buttery. I think two things fixed that. One, I used regular (salted) butter that first time as I didn't have any unsalted... big mistake! It really did make a difference using unsalted. Two, I used FromScratchSF's method of mixing on slow speed only, with really soft butter, that made a difference to the taste too. Also the recipe said I could expect 4-5 cups, I got SIX cups after switching to her technique.
Thanks FSSF, you probably don't realise how many people like me really appreciate the time you take to educate us, your generosity in sharing your techniques has made the world of difference for me.
rlowry, you mentioned adding white chocolate. I added both vanilla AND white chocolate to some IMBC last night, and it was delicious! I suspect I may want to do that to every single batch from now on
Just make sure you melt your chocolate in advance so it has time to cool down somewhat before adding in. If it's a lot hotter than your icing, then it will cool too quickly and you'll have lumps of chocolate in your icing.