This whole icing sets hard. I use it to ice my Christmas fruit cake. Use it to glue together and decorate gingerbread house.
Beat egg whites until stiff.
Gradually add icing sugar.
Add lemon and/or vanilla.
For fruit cake, cover cake with apricot jam and then Marzipan, making sure the marzipan seals the cake. Leave to dry overnight, and then ice with Royal icing. Leave open to the air overnight to allow to set hard.
This icing dries hard and dries easily. It can be piped easily. Keep it covered while you work with it for making gingerbread house.