[header] How to decorate an ice cream cake [title] Freeze the cake for at least 3 hours before icing it. [step] You want your ice cream cake to stay together while you're icing and decorating it, which is why keeping it as frozen as possible is important. [title] Pick out a frosting that complements a frozen cake. 
[step] Most normal buttercream frostings will crack or break once they're frozen. A whipped cream topping is the best choice-it will stay nice and smooth after being used.