Put the rock sugar in a large glass with a lid. Squeeze the 6 oranges, cut into quarters and pour into the glass with the juice. Crush the tonka bean in a mortar and place in the glass. Also pour the vanilla pod, cloves, star anise and cinnamon stick into the glass, fill up with the rum and stir thoroughly once.
Let it steep for 3 weeks on a sunny windowsill and stir every 2 days in between. Then filter through a hair sieve and fill into bottles.