Fondant is one of the most popular icings. Cake decorators use it not only to cover cakes but also to make figurines, flowers and other decorative items to put on cakes. Fondant tends to take a while to set hard, so if you are making a fondant crown for a cake, do so at least a week before you need it so that there is adequate time for it to harden.
Draw a template for the crown on paper and cut around it with scissors. A simple crown shape would be flat on one side, with around an inch or two thickness for the band and a triangular peak in the centre.
Leave the fondant out on a bench, covered with a towel, until it is room temperature and pliable.
Sprinkle cornstarch onto a clean counter and knead the fondant for a minute. Roll out a piece of fondant to 1/8 inch thick. Make the piece long and wide enough for the crown template to fit on top.
Place the crown template on top of the fondant and cut around it with the tip of a knife or with fondant cutters. Remove the template.
Dust the bottom half of a plastic cup or jar with cornstarch and then wrap the fondant crown piece around the bottom of the cup or jar so that it dries in a circle. Dab a tiny bit of water onto the ends of the crown piece and stick them together to form the full circlet of the crown.
Decorate the crown with edible decorations, such as sugar pearls or candy jewels. Use buttercream icing as glue if necessary. Leave the crown around the cup or jar to harden. Depending on the humidity and temperature in your area, hardening can take up to five days. Remove the crown from the cup or jar and place it on the cake.
If it is very humid or if you want to be sure of a hard crown overnight, knead in about a tablespoon of tylose powder per pound of fondant, which will increase the hardening ability of the fondant.
Do not place the fondant crown in the refrigerator, as this will increase the moisture content of the fondant and cause it to sag or lose shape.