"Gingerbread house icing you can eat. It holds together really well! To use, place in piping bag or use spatula to spread onto the gingerbread house pieces to stick them together. This icing can also be used to decorate the tops of cookies."
Beat both amounts of meringue powder, 1 cup warm water, cream of tartar, and confectioners' sugar in a large bowl using an electric mixer on low. Scrape down sides of bowl and increase mixer speed to medium; beat until fluffy and shiny, 6 to 8 minutes. If frosting is too stiff, beat in 2 tablespoons warm water, or as needed, adding water in small amounts. Keep frosting covered with a damp towel until needed.
I usually will reserve the 2 tablespoons of warm water until the end, to use to get the desired consistency. If the icing is too runny, add more powdered sugar. If the icing is too stiff, add more water in very small amounts.