Make the frosting just before you serve the cake and only ice as many cakes as you need. Store the frosting (and any iced cakes) in an airtight container in the fridge. The frosting will keep for ...
Ready-made icing can be bought from most supermarkets, but it is easily made at home: the core ingredient, icing sugar, is widely available. When making fat-based icings such as buttercream ...