What must happen to marshmallow icing before being applied to cakes?

Marshmallow icing must be cooled completely before being applied to cakes to ensure that it adheres properly without causing any damage to the cake itself. When marshmallow icing is hot, its consistency is too fluid, which can lead to it sliding off or not sticking effectively to the cake layers. Additionally, applying hot icing could melt or distort the cake layers, especially if they are delicate or frosted.

Cooling the icing allows it to reach the right spreadability without risking the integrity of the cake. Once cooled, the icing can be whipped to achieve a fluffy consistency that spreads easily and provides an appealing look and texture to the finished pastry item.