Easy Icing for Gingerbread houses

We have the tradition of making and decorating a gingerbread house each year for christmas and over the last three years I have perfected my gingerbread house icing so that it can withstand the children's decoration.

Ingredients:

• 2 egg whites
• 2 teaspoons cream of tartar 
• Icing sugar (as required)

Method:

1. Whisk the egg whites until they are forming soft peaks
2. Add the cream of tartar and start to whisk in icing sugar
3. Now you will see that there is no measurement for the amount of icing sugar to be added.this is as it is really dependent on the size of your eggs.  
4. What you are looking for is a firm icing that can be piped on to the house for decoration, but also used for mortar.