Make Simple Syrup Mixture - combine equal parts of water to sugar in a non-reactive sauce pan. Boil until sugar has dissolved in the water. Remove syrup from heal and let cool to room temperature. Note: You may substitute vanilla sugar for plain sugar if you like.
Cut vanilla bean in half lengthwise. Make sure they vanilla beans are fat, pliable pods that feel heavy. Avoid using brittle or dried up beans.
Pour off ½ cup of rum from bottle and save in different container for future use.
Add cut vanilla beans into bottle.
Pour in Simple Syrup Mixture to bottle.
Let mixture sit for at least one month. The flavor will continue to get better with age.