Let us know how the ganache works out when you try it again!

I make ganache often but I just melt the chocolate and let it cool and put it in the fridge. I don't rewhip at all and is great for fillings. If I use it over cakes I just get it to room temperature and pour over cakes.

That's one type of ganache Mariu, sure...."poured ganache". But "whipped ganache" makes an entirely different icing. It becomes, fluffier & matte...more delicate really.

I've done wedding cakes iced in whipped ganache. It's really pretty, but man oh man it's tricky to whip up without over-whipping like the OP did and even harder to smooth. I won't do it often.

I tend to stick with whipped ganache as either a filling, or use as an icing on fondant cakes only, since it's hard to smooth.

As far as the clumping goes, I'd agree with previous posters that it was overwhipped. I'm always shocked at how quickly mine gets to the right consistency. I just use my hand mixer in the same pot I boil the cream in - it's not worth getting out the big KA for just a few seconds! I'd say mine usually reaches the right consistency in less than a minute.

I generally do equal parts chocolate and cream (by weight), which makes a thinner ganache to begin with.

Yep, I agree with the over whipping. I chill mine overnight and whip with my hand mixer instead of the KA.

Yeah you definitely just overwhipped it, as mentioned watch for the colour to start to change then slow the speed down and be careful just like when whipping fresh cream it will turn and go too far in a second.