Strain garbanzo beans from both cans and set aside for your own use later. Boil the juice for about 5 minutes until it's reduced to a 1/2 cup. Cool and strain through a find mesh sieve.
Using a stand mixer with a whip attachment or a handheld with single whip, beat the boiled juice for about 2 minutes. It will become foamy and doubled up in size. Add 2 cups of powdered sugar and whip for 2 minutes. Add the rest of the sugar 1 cup at a time whipping 1 min each time. Add in the vanilla. Whip until shiny and glossy and stiff peaks form when you lift the whip out of the mixture.
Pour out onto plastic wrap and fold over ends to create a pouch. Tightly wrap both ends in opposite directions to seal up the frosting balloon. See Video. Snip end and pop into a frosting bag to pipe onto cooled cookies.
The royal icing dries a bit slower than its traditional counter part