White ganache from cocoa butter won't set I want to create white truffles which doesn't taste like white chocolate (sugar and vanilla) but like dark chocolate. So I tried to create them from cocoa butter. 

I added 60 g of cocoa butter, 17g of cream and 12g of powdered sugar (because it tasted sugary enough) and a little of salt. The problem is when ganache cooled down it was made from 2 layers. Hard top and quite liquid bottom. I could add more cream but I am afraid that the bottom would be more liquid and the top would be the same.
Maybe the problem is that most recipes for white chocolate from cocoa butter needed milk powder (which is very expensive) or egg white powder (which is also expensive) and I did ganache without them. Do I need an emulsifier? I have soy lecithin and some others modern thickeners.

I can made truffles from dark chocolate without problem.
What you're missing is solids. 17g of cream (especially when you consider the high percentage of fat in cream in relation to solids) is not going to be enough against 60g of cocoa butter. Where are you from? In the US, milk solids (in the form of dried milk powder) are cheap compared to cocoa butter. Many high quality white chocolate brands do not contain any kind of emulsifier, but all contain a significant volume of solids. Those solids are almost always milk, with the exception of a few specialized vegan varieties.

I'm wondering in what way you are trying to emulate dark chocolate, since the difference between dark chocolate and white chocolate is cocoa solids (the dark stuff)?