How does one do this to ensure the buttercream icing doesn't melt?
Make sure the ganache is cool enough first.
Chill the cake, too. that will make the ganache firm up faster, though, so you have to work fast.
Anyone have a preferred recipe?
For ganache? I think it's 2:1 ratio dark chocolate to heavy cream (by weight) and 3:1 for white chocolate. You can add more or less of each ingredient to adjust how thick it is, but that's the basic proportion to use.
That is what I have used for other recipes that call for ganache.
Is there a recommend temp to cool to before pouring over buttercream so that it is cool enough, but still workable?