AIt looks like they piped on the icing with royal, let it set, then over painted with lustre dust.
Here's a tutorial: https://www.sweetambs.com/tutorial/gold-royal-icing/
ALooks like delicate piping to me, and freehanded. Royal icing, with gold highlighter painted on after the RI dried.
AI'd cover in fondant if I were you, give that fine piping a smooth and clean as possible background as possible.
AThat was a lot of possibles...lol
I use the gold spray, you buy it in a can and spray it in a small plastic shooter glass, then I use that as paint with a paint brush.
I read that the highlighter dust is not edible. But I have seen that gold foil 23-24kt are food safe. What is the difference?