How can I avoid chocolate truffle mix curdling?
I have made a lot of truffles, and even more ganache for other purposes, and I have never had this happen. My guess is that you are boiling the cream too hard and that is causing the curdling.

How to make ganache:
You will need by weight one part 35% cream to 2 parts chocolate of your choice.

Chop your chocolate (if it's in blocks or chunks), put into a heatproof bowl (stainless steel is best) away fro your heat.

In a saucepan or pot (depending on how much you're making), bring the cream up to a high simmer. 

Pour the cream immediately over the chocolate and stir with a silicone spatula if you have one, a wooden spoon otherwise. The chocolate should completely melt within about two minutes; longer for very high percentage dark chocolates. At this point if you are making flavoured truffles, add your flavourings (unless your flavour compounds have been infused into the cream). 

Chill until set, make into truffles.

Edited to add:

If you are using alcohol as a flavouring in your truffles, you will need to use either more chocolate or less cream. I have found that approximately for every fluid ounce of alcohol added, remove 3/4-1 fluid ounce of cream from the recipe. I prefer to infuse flavourings in the cream, and have had great success with beets, bacon (with a Guinness reduction added to the chocolate later), black truffle and pureed walnut, and honey. Be sure to strain, of course, before adding the hot cream to the chocolate.

I have also found that white chocolate will often need slightly less cream than a milk or dark.