What type of decorative paste is made with sugar, cornstarch, and gelatin?

The correct answer is Pastillage. This type of decorative paste is specifically known for its ability to harden and create intricate sugar decorations. Pastillage is a mixture of sugar, cornstarch, gelatin, and water, which makes it versatile for crafting decorations such as flowers, figurines, and other edible adornments that are not only visually appealing but also durable.

Fondant, while also made from sugar, is primarily used for covering cakes and creating smooth finishes rather than for hardening into shapes. Marzipan is a sweet almond paste typically used for modeling and decorating but does not include cornstarch or the same hardening qualities as pastillage. Royal icing, made with egg whites or meringue powder and powdered sugar, is used for piping and decoration but has a different texture and composition and does not contain cornstarch or gelatin.