Place cinnamon and cardamom pods in a large stock pot. Turn the heat to medium and toast the spices for about 5 minutes, or until fragrant. 

Add sugar and vinegar and bring to a very low simmer. Stir until the sugar is completely dissolved. About 5 minutes. Remove from heat and set aside. 

Use a fork to puncture each plum. Fill Weck Jars (or any mason jar) 1/2 full of plums. Pour the liquid over the plums, so that they are completely covered, but leaving 1/4" head space. 

Seal each jar tightly and refrigerate until needed.