The ratio is not clear to me for the white chocolate ganache.
It's 3:1 for white chocolate, is that cups or weight?
It's 3 to 1 by volume. I use the recipe in the Planet Cake book. Comes out great, especially since I got a small electronic kitchen scale so that I can do it by volume.
3:1 for White and milk
2:1 for dark
I use for example, 400g dark: 200ml cream. 600g White: 200ml cream etc...
so... using the example of 600 g white choc to 200 ml cream, how much ganache does that make?
Is it enough to torte and ice a 10' cake, or torte or ice only?
Measure by weight, not volume, for both the chocolate and the cream.
Here's another topic about ratios that may help you. EnglishCakeLady has posted a link to a ganache calculator which tells you how much ganache to make for each different sized cake. Click on the link and it will download an excel file to your computer.