What is the best method to making stained glass on a fondant cake? Royal icing outlines and piping gel? Thanks!
That's exactly what I was going to suggest. That's how I did my stained glass cake in my photos.
That's what I've done (works on buttercream, too). It actually comes out beautiful because the piping gel stays shiny so it looks like the sun is shining through, plus it's transluscent, like real stained glass.