Wash the fig leaves well, put them in a deep pot with 4 1/5 cups (1 L) boiling water.
Leave to boil for 20 min., then remove from the heat. Once cooled, strain the concoction through a cheesecloth.
Put it on the stove again and boil another 20-30 min. on low heat with the crystal sugar. Add 1 packet of vanilla sugar or 2 packets of powdered vanilla.
Finally add in 1 packet citric acid.
While still hot, pour the syrup into juice bottles, close tightly and leave upside down to vacuum seal the caps.
When serving, you can dilute with carbonated or regular water.
The ingredients yielded me 4 bottles of 1 cup (250 ml) each.