Edited: Made the question a little less rambling.
I always thought that icing a cake was a pretty simple process. And then I tried to actually do it. Oh boy, how wrong I was!
It sounds simple enough. You take some icing sugar, wet it, mix it up until it's smooth, and then cover your cake with the stuff.
The problem is, when I do this, the icing always runs off the top of the cake.
Each time I make icing, I make it even drier than the last time. (Although never as little as 3 tsp per 100g. If you do that, it's just powder. I got 4 tsp to work though.) I've now reached the point where the icing is so thick and goopy that I struggle to mix it, and it's murder to stop it sticking to everything it touches - the bowl, the spoon, etc. And yet, it still runs off the cake!
Question: How to prevent glacé icing from running off the cake?
Obviously the pros always get this right every single time without fail. But how do they do that? Is it just that I need 30+ years of trial and error in order to instinctively "know" what the correct consistency is? Or is there something more specific?
PS. I realize I could use butter cream or fondant instead of glacé icing. (In fact, I'm probably going to do that at some point.) But plenty of professional cakes use glacé icing, so it must be possible, and I'm curious to know how.
PPS. No, the cake isn't particularly flat on top.