Hi,
I will be adding raspberry pie filling to my buttercream, which will be shortening based. I'd like to know the pie filling to buttercream ration to follow?

I made a test batch using Rick's special buttercream http://cakecentral.com/recipes/15014/ricks-special-buttercream-2
but the I think I added too much filling and the buttercream ended up curdled and very thin.

Thanks.