Thank you Tessa - I love you!!
I didn't quite believe it could work and only because I trust my good friend Tessa with my life did I dare to try it....
Pretty much any chocolate (oddly) in any amount - 4 minutes at 40%. Perfect. Even when you include butter too; even white chocolate, although it still then misbehaves on contact with butter (see earlier ramblings).
All that faffing about with bain maries is SO OVER.