Combine the licorice, sugar and 150 ml (5 fl oz) water in a small saucepan over very low heat and cook, stirring occasionally, until the licorice is dissolved and the mixture is smooth, adding a little more water, if necessary. Working quickly, transfer to an upright blender and blend until smooth. While still hot, pass through a fine sieve. Place in a container and store at room temperature.
This can be made 1 day in advance.