How do I get the butter out of my chocolate fondue?
The short answer is:  you cannot get the butter out.  The milk solids from the butter will be throughout the mixture, and the sheen on top may not be just milk fat from butter, but some cocoa butter as well.   Even if you do try to skim the butter off the top, the remaining chocolate will never have the same quality as it did before.

Some options:


Reheat it for more fondue based enjoyement
Add cream or milk, and use the remainder as a sauce over ice cream or another desert
You have not mentioned if there are any other ingredients in the chocolate fondue mixture.  Assuming it is only chocolate and butter, estimate the ratio of chocolate to butter.  You could then probably use it to replace some proportion of butter and chocolate in certain brownies or cookies.


Truthfully, either of the first two choices are your best option.  It should also freeze fairly well if you want to hold it for a future fondue party.