Combine sugar and orange zest in a large mortar or small bowl.
Mix well with the back of a wooden spoon or the pestle of the mortar until the orange zest is no longer visible.
Pour into the container to infuse, pour cognac over the top. Let steep in a cool, dark place for three months, shaking well once a month.
Pour the mixture through a fine sieve, rinse the container well.
Add glycerine to the vessel. Filter the mixture through a fine filter or possibly a juice bag to the glycerine.
Stir well with a wooden spoon. Seal and allow to infuse for three more months.