I'd like a chocolate lining in a banana cream pie, very similar to this recipe. However, I notice in the final pie that the chocolate lining is a little on the bitter side. What is a good way to sweeten it up? I'm no expert on ganache, but my understanding is I shouldn't just add sugar as it will turn grainy. If I melt sugar into the cream before the chocolate, how much should I use?
While adding sugar syrups like corn syrup or invert syrup to ganache is fairly common, it will change the texture of the ganache. You'd end up with something more like a chocolate coating.
If bitterness specifically is the problem, I'd suggest using a less bitter chocolate. Perhaps you can find something with lower cocoa solids that will have a smoother flavor without adding any sweeteners.
Added from a comment since I remembered: A tiny amount of salt can also help to cover bitterness. You could try that.