i only made ganache one other time, in which i let it cool then whipped it.
so this is the first time i am using it warm, to drip over the edge of a buttercream frosted cake.
i need this for tomorrow.
so yesterday i had a small practice cake in my freezer, i let it thaw, frosted it, then tried out the ganache, using a one to one ratio of chocolate to cream. maybe i should have used less cream.

i heated the cream in the microwave to just boiling, then poured it over the dark chocolate chips.
first problem is that when the chips were all melted, there were flecks of darker chocolate, and a few small lumps that wouldnt melt. so it wasnt smoothe, like the first time i made it.

i put the bowl in the refrigerator to cool it down, frequently stirring it, waiting for it to thicken. it took forever to get to the point where it wasnt too runny. i poured it on the cake, it still seemed too runny, so i put it back in the refrig to cool more. it looked ok on the cake, but was thin, and you could see the pink buttercream through it. so i chilled it again, planning to put another thicker layer on the cake. after about an hour it finally looked like the right consistency (but still had the small flakes and lumps), so i poured some on the cake, and it caused the original thin layer to slide off, exposing the pink icing underneath.

i'm making a new cake today, will put the buttercream frosting on it tonight and refrigerate it (because it will have whipped cream and strawberries between the layers). tomorrow, i plan to take it out of the fridge, make the ganache, and pour the ganache over it.

questions:
1) should i bring the cake to room temperature before pouring the ganache, or pour it on a cold cake?
2) how do i prevent the flecks from forming, and the small chunks?
3) will the ganache melt some of the buttercream, or did i only have that problem because i tried to ganache the cake twice?
4) will refrigerating the cake after the ganache is on, hurt the ganache?

I'm not sure why the chocolate didn't melt, but if whisking doesn't help the pieces melt and incorporate, you can pour it through a strainer.

One part chocolate and one part cream is probably ok be sure the ratio is by weight. 1 cup of cream is 8 ounces so the chocolate would be 8 ounces.

You don't need to refrigerate the fresh ganache, but it will take a bit longer to cool enough to not melt the icing.

To control the drips down the side, you can use a squeeze bottle to apply the chocolate.

Refrigerating the finished cake will not harm the ganache, but it will lose a bit of its shine.

1) Probably. My thinking is that once that ganache hits a cold cake, it will immediately start to thicken. That may not be what you want for a drizzled effect.

2) Never had this happen. Once you pour the heated cream over the chocolate, you should stir until smooth. Maybe you need to use better chocolate?

3) How hot was the ganache. If it's too warm then yes it might melt your buttercream. It probably needs to be room temp.

4) No, not in my experience

thanks for your responses.
maybe i didnt measure right, i might have had more cream to chocolate.
i'll try again tomorrow. if it doesnt turn out right, i'll just put the chocolate dipped strawberries on top like i planned to anyway, but would still like to see ganache dripping down the sides.
i'll let you all know how it turns out.

Ive never made ganache, but here is something Ive learned from dipping things in chocolate:

It is possible to heat chocolate so much that it will lump (that is opposite of what we usually think). It will clump up and not seem to "melt" when in reality it is so overheated it has become something other than chocolate. In this case, it is VERY hot...way hotter than you think. It is holding in the heat. It will take a long time to cool and would thus melt yor buttercream. In addition, it may never reconstitute to the creamy chocolate you want.

Try it with less heat and allow the chocolate to melt slowly, then stir.