Take Guava puree, sugar, lemon juices, and spices (if using) in the thick-bottomed pot.
Cook jam for about 30 minutes on medium heat with occasional stirring. Once the jam starts to thicken stir frequently. (Vigilant observation will be necessary as the jam reaches the setting point.)
The jam is ready when you see the bottom of the pot clearly while stirring. Another tip is when you draw a line on the spatula, the jam will coat the spatula thickly. (Do not overcook or the sugar might caramelize and burn to make the jam bitter.)
Remove cinnamon sticks and cardamom pods from the jam.
Transfer hot jam plum jam to clean and preferably sterilized jars. Seal the lid and turn the jars upside down.
Store in the fridge if consuming immediately. Or follow proper sterilization steps and seal it for canning and follow the water bath procedure if intending to store it in the pantry for a longer period. Or let the jam cool completely for 12 hours then freeze.