Mix the elderberry juice and rock candy in a saucepan and heat on medium heat, melt the rock candy in it. Then add the almond flavor and vanilla sugar. Turn off the stove and take the pot off the stove. Pour the rum into the pot, put the pot back on the warm stove, but DO NOT let it boil anymore. Let cool and fill into bottles. Let it steep for a few days / weeks, depending on your taste.