Royal Icing for Graham Cracker Gingerbread Houses (The best "glue")

0 Rinse your mixing bowl with lemon juice or white vinegar.
2 Beat the egg whites and cream of tartar at high speed until they are foamy.
4 Add the sugar and lemon juice.
6 Beat at high speed until thick and fluffy.
8 You may need to add a little water if it is too stiff or a little sugar if it is too thin. It should have the texture of old fashioned paste.