In a saucepan, bring the sugar or rock candy with water and the chopped tonka bean to a boil. Let the whole thing simmer for about 20 minutes - do not put a lid on the pot! When the syrup is ready, pour the liquid through a fine-mesh sieve and pour it into a clean bottle.
The syrup tastes very good in coffee or tea.
Tonka beans have a slight taste of vanilla and marzipan and are harmful in large quantities!