What should you use to make a star on top of a Christmas tree on a cake?
You can color gum paste yellow, cut out a star, and allow it to
dry for a few days. I don't know if your cake is 2d or 3d, but if
the star needs to stand up, you can put a skewer in the middle of
the gum paste before you leave it to dry. Then you can just poke
the skewer into the cake to make the star stand up. If you want a
gold star, you can leave the gum paste white and paint the star
with a combination of vodka and gold luster dust.