>>11211
>What is the difference between those 2 techniques?
One uses a double boiler. The other one is easier, but creates a slightly lower quality ganache.
> And do i need to add sugar is the chocolate is 70% and it is dark?
If you are starting with "eating" chocolate (as opposed to baking chocolate), you don't need to add sugar. Check the ingredients on your chocolate… if there is sugar in there, you don't need to add any. I would normally go with about 3 or 4 parts bittersweet or dark chocolate to 1 part semisweet or milk chocolate anyway.
> or does the milk/cream make it not bitter?
Unsweetened chocolate is going to be bitter, but the fat and sugar (lactose) in the milk is going to make your tongue not care so much. Softens the edge a bit; eliminates that tongue-drying intense bitterness and leaves a mild pleasant bitterness in its place. Thank goodness you can taste test as you go.
Chocolate is finicky about extra moisture; be quite careful to keep the steam from the double boiler out of the top bowl. This is the main advantage for the method of pouring hot cream onto the chocolate and melting with residual heat - not likely to drip water in. Downside is that with the typical proportions, it's a quite soft ganache, requiring chilling to keep solid.