How best to toast/brown marzipan? The recipe/picture that I'm following calls for cutting out Christmas stars from marzipan and for the stars to be browned somewhat (does look nice).

Last time I did this, the stars deformed quite a lot and lost the sharpness of their points, as the marzipan melted and softened.

So, for something prone to melting like marzipan is it best to toast quickly / high heat or  more gradually? Any ideas?

I'm just grilling them under heat.
Either use a blow torch or a very hot grill. Either way be very careful as it can burn extremely easily. I've only ever done it with balls of marzipan (on top of a simnel cake), so haven't had deformation issues, but I would suggest blowtorching the marzipan in the cutter, then letting it cool to prevent the points softening.